Five Prime Therapeutics (FPRX) 424B5 Prospectus supplement for primary offering

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-228206

PROSPECTUS SUPPLEMENT

(To Prospectus dated August 22, 2019)

7,200,000 Shares

Common Stock

We are offering 7,200,000 shares of our common stock. Our common stock is listed on The Nasdaq Global Select Market under the symbol “FPRX.” On November 12, 2020, the last reported sales price of our common stock on The Nasdaq Global Select Market was $22.43 per share.

Investing in our common stock involves risks. Please see “Risk Factors” beginning on page S-6 of this prospectus supplement for more information and in the documents incorporated by reference into this prospectus supplement and the accompanying prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

	Per Share		Total
Public offering price	$	21.00	$	151,200,000
Underwriting discounts and commissions(1)	$	1.26	$	9,072,000
Proceeds to us, before expenses	$	19.74	$	142,128,000

(1) See “Underwriting” for additional disclosure regarding underwriting discounts and commissions and other estimated offering expenses.

We have granted the underwriters an option for 30 days from the date of this prospectus supplement to purchase up to 1,080,000 additional shares of our common stock on the same terms as set forth above.

Delivery of the shares of common stock in this offering is expected to occur on or about November 17, 2020.

Cowen		SVB Leerink
	Wedbush PacGrow

The date of this prospectus supplement is November 12, 2020.

TABLE OF CONTENTS

Prospectus Supplement

	Page
About this Prospectus Supplement		S-1
Prospectus Summary		S-2
The Offering		S-5
Risk Factors		S-6
Special Note Regarding Forward-Looking Statements		S-8
Use of Proceeds		S-10
Dividend Policy		S-11
Dilution		S-12
Material U.S. Federal Income Tax Consequences to Non-U.S. Holders		S-14
Underwriting		S-18
Legal Matters		S-25
Experts		S-25
Where You Can Find More Information		S-25
Incorporation of Certain Information by Reference		S-25

Prospectus

ABOUT THIS PROSPECTUS	ii
PROSPECTUS SUMMARY	1
RISK FACTORS	3
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	4
USE OF PROCEEDS	6
DESCRIPTION OF CAPITAL STOCK	7
PLAN OF DISTRIBUTION	11
LEGAL MATTERS	13
EXPERTS	13
WHERE YOU CAN FIND MORE INFORMATION	13
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	13

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ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus are part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process, and that was declared effective on August 22, 2019. This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this common stock offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference herein. The second part, the accompanying prospectus, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. To the extent there is a conflict between the information contained in this prospectus supplement and the information contained in the accompanying prospectus or any document incorporated by reference therein filed prior to the date of this prospectus supplement, you should rely on the information in this prospectus supplement; provided that if any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in the accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement. Generally, when we refer to the prospectus, we are referring collectively to this prospectus supplement and the accompanying prospectus.

We have not, and underwriters have not, authorized anyone else to provide you with any information other than that contained or incorporated by reference in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein and any information contained in any free writing prospectus we have authorized for use in connection with this offering. We have not, and the underwriters have not, authorized anyone else to provide you with different information. We take, and the underwriters take, no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We are offering to sell, and seeking offers to buy, shares of our common stock only in jurisdictions where offers and sales are permitted.

The information contained in this prospectus supplement, the accompanying prospectus, the information in the documents incorporated by reference in this prospectus supplement and the accompanying prospectus, and any authorized free writing prospectus is accurate only as of the date of those respective documents, regardless of the time of delivery of this prospectus supplement and the accompanying prospectus or of any sale of shares of our common stock. Our business, financial condition, results of operations and prospects may have changed since those dates. It is important for you to read and consider all information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus in making your investment decision. You should read this prospectus supplement and the accompanying prospectus, as well as the documents incorporated by reference into this prospectus supplement and the accompanying prospectus, and any authorized free writing prospectus. You should also read and consider the information in the documents we have referred you to in the sections of this prospectus supplement titled “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

Except as otherwise indicated herein or therein or as the context otherwise requires, references in this prospectus supplement and accompanying prospectus to “Five Prime,” “the company,” “we,” “us,” “our” and similar references refer to Five Prime Therapeutics, Inc. The Five Prime logo is our registered trademark. This prospectus supplement and the accompanying prospectus, including the information incorporated by reference into this prospectus supplement and the accompanying prospectus, and any free writing prospectuses we have authorized for use in connection with this offering, contains registered marks, trademarks and trade names of other companies, which are the property of their respective owners.

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PROSPECTUS SUMMARY

This summary highlights selected information about us, this offering, and selected information contained elsewhere in or incorporated by reference into this prospectus supplement and the accompanying prospectus. This summary is not complete and does not contain all of the information that you should consider before deciding whether to invest in our common stock. For a more complete understanding of our company and this offering, we encourage you to read and carefully consider the more detailed information contained in this prospectus supplement and the accompanying prospectus, including the information incorporated by reference herein and therein, and the information in any free writing prospectus that we have authorized for use in connection with this offering, including the risks described under the section titled “Risk Factors” in this prospectus supplement and the accompanying prospectus and in our Quarterly Report on Form 10-Q for the quarter ended September 30, 2020, as updated by our subsequent filings under the Securities Exchange Act of 1934, or the Exchange Act, each of which are incorporated herein by reference.

Company Overview

Our Company

We are a clinical-stage biotechnology company focused on developing immune modulators and precision therapies to improve the lives of patients with solid tumor cancers. Our primary focus is on developing immuno-oncology and targeted cancer therapies. Each of our product candidates has an innovative mechanism of action and addresses patient populations for which better therapies are needed. In addition, we use companion diagnostics where appropriate to allow us to select patients most likely to benefit from treatment with our product candidates. The most advanced product candidates that we or our partners are developing are identified below.

• Bemarituzumab (FPA144) is an antibody that inhibits fibroblast growth factor receptor 2b, or FGFR2b, and that induces antibody-dependent cell-mediated cytotoxicity that we are studying in a Phase 2 clinical trial in combination with 5-fluorouracil (5-FU), leucovorin and oxaliplatin, a standard-of-care chemotherapy regimen known as mFOLFOX6, as front-line treatment of patients with FGFR2b+, non-HER2+ gastric (stomach) or gastroesophageal junction, or GEJ, cancer. In December 2017, we granted Zai Lab (Shanghai) Co., Ltd., or Zai Lab, an exclusive license to develop and commercialize bemarituzumab in China, Hong Kong, Macau and Taiwan.

• FPT155 is a soluble CD80 fusion protein that enhances co-stimulation of T cells through CD28 that we are studying in a clinical trial in multiple cancers.

• FPA157 is an anti-CCR8 antibody that is engineered to deplete CCR8-expressing intratumoral regulatory CD4+ T cells. We are conducting IND-enabling activities for FPA157 and plan to file an IND in the first half of 2022.

• BMS-986258 is an anti-T cell immunoglobulin and mucin domain-3, or TIM-3, antibody that our partner, Bristol-Myers Squibb Company, or BMS, is studying in a clinical trial in combination with Opdivo^® (nivolumab) in patients with advanced malignant tumors.

Our product candidates are typically only-in-class, first-in-class or meaningfully differentiated from other in-class therapeutics. We generally look for single-agent activity or clear activity in, for example, tumor types that are rarely sensitive to checkpoint inhibitors.

We have three preclinical and late-stage research programs, including FPA157. These programs arose from our prior in-house target discovery and validation and protein therapeutic generation and engineering capabilities, which we eliminated in 2019. We expect to advance each of these programs through preclinical development

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relying mostly on out-sourced and contracted capabilities. In addition, we plan to supplement our product pipeline by looking to selectively acquire or license, on an exclusive basis, rights to product candidates from biotechnology and pharmaceutical companies.

We have no products approved for commercial sale and have not generated any revenue from product sales to date. We continue to incur significant research and development expenses related to our late-stage research programs and our preclinical and clinical product candidates and other expenses related to our ongoing operations. We expect that, if we do not partner our programs, our expenses will increase as we advance our product candidates into later stages of clinical development and increase the number of product candidates in clinical development. We have incurred losses in each period since inception of operations in 2002, with the exception of the fiscal year ended December 31, 2015, due primarily to the $350.0 million up-front payment we received from BMS under our license and collaboration agreement for cabiralizumab, and the fiscal year ended December 31, 2011, due primarily to the $50.0 million upfront payment we received from Human Genome Sciences, Inc. from a license and collaboration agreement for FP-1039, a product candidate we were developing at the time. For the nine months ended September 30, 2020 and 2019, we reported a net loss of $63.5 million and $105.8 million, respectively.

Product Pipeline

The following table shows the stage of development of the most advanced product candidates that we are developing or that have come from our pipeline and are being developed or supported by our collaborators:

* Partnered with Zai Lab – see “Part I—Item 1. Collaborations” of our Annual Report on Form 10-K for the year ended December 31, 2019, which was filed with the SEC on February 27, 2020, or our Annual Report, for a description of our China collaboration agreement with Zai Lab.

** Partnered with BMS – see “Part I—Item 1. Collaborations” of our Annual Report for a description of our collaboration agreement with BMS.

^‡  We are in the process of amending the FIGHT trial from a Phase 3 design to a randomized Phase 2 trial. For additional information, see the description of our bemarituzumab program our Quarterly Report on Form 10-Q for the quarter ended September 30, 2020, which was filed with the SEC on November 3, 2020.

† Development is being conducted exclusively by BMS.

†† Development is being conducted exclusively by Seagen Inc.

Recent Events

In November 2020, we announced that all three primary and secondary endpoints in our global, randomized, double-blind placebo-controlled Phase 2 trial of bemarituzumab in combination with mFOLFOX6 as front-line

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treatment of patients with advanced FGFR2b+, non-HER2+ gastric and gastroesophageal junction, or GEJ, cancer, which we refer to as our FIGHT trial, met pre-specified statistical significance (at a 2-sided alpha of 2.0) as compared to placebo in combination with mFOLFOX6. The primary endpoint in the FIGHT trial was progression-free survival, or PFS, and the secondary efficacy endpoints were overall survival, or OS, and objective response rate, or ORR. The FIGHT trial was designed to evaluate the safety and efficacy of bemarituzumab in combination with standard-of-care mFOLFOX6 chemotherapy as compared to placebo in combination with mFOLFOX6 chemotherapy in front-line gastric and GEJ cancers. The FIGHT trial enrolled 155 patients in 15 countries across Asia, the European Union and the United States.

We identified patients for inclusion in the FIGHT trial using both an immunohistochemistry, or IHC, test, which allowed us to detect FGFR2b overexpression on the tumor tissue in a biopsy specimen, and a ctDNA blood-based test, which allowed us to detect FGFR2 gene amplification from DNA shed by tumor cells in blood plasma. FGFR2 gene amplification is a cause of FGFR2b overexpression, and measuring FGFR2 gene amplification in the blood is an indirect way of identifying tumors that overexpress FGFR2b that we may otherwise not identify using an IHC test. We excluded from eligibility for the trial any patients known to be HER2+. We screened over 900 patients and found that approximately 30% of non-HER2+ gastric and GEJ cancers overexpress FGFR2b. The frequency of FGFR2b overexpression was similar across Asia, the European Union and the United States.

Top-line data from the FIGHT trial show the following efficacy results for bemarituzumab in combination with mFOLFOX6 as compared to placebo in combination with mFOLFOX6:

• an increase in median PFS from 7.4 months in the placebo arm to 9.5 months in the bemarituzumab arm (hazard ratio 0.68; 95% confidence interval 0.44 – 1.04; p = 0.073);

• an increase in median OS from 12.9 months in the placebo arm to not reached in the bemarituzumab arm (hazard ratio 0.58; 95% confidence interval 0.35 – 0.95; p = 0.027); and

• an improvement in ORR of 13.1%, from 33.3% in the placebo arm to 46.8% in the bemarituzumab arm (95% confidence interval -29.0% to 2.8%; p = 0.106).

The incidence of all of the following adverse events was comparable between patients in the bemarituzumab treatment arm and patients in the placebo arm of the study: adverse events of any grade (100% vs. 98.7%, respectively), serious adverse events (31.6% vs. 36.4%, respectively) and deaths due to adverse events (6.6% vs. 5.2%, respectively). Treatment-emergent adverse events that were grade 3 or higher were more frequently reported in patients receiving bemarituzumab in combination with mFOLFOX6 (82.9%) as compared to patients receiving placebo in combination with mFOLFOX6 (74.0%).

As expected, corneal and stomatitis adverse events were more frequently reported in patients receiving bemarituzumab in combination with mFOLFOX6 as compared to patients receiving placebo in combination with mFOLFOX6, and more patients discontinued bemarituzumab (34.2%) compared to placebo (5.2%) due to an adverse event. There were no reported treatment-emergent adverse events of retinal pigment epithelial detachment or hyperphosphatemia in patients receiving bemarituzumab in combination with mFOLFOX6. Despite the higher frequency of discontinuation of bemarituzumab compared to placebo, all efficacy endpoints favored bemarituzumab. For future clinical trials of bemarituzumab, we plan to work closely with investigators and advisors to incorporate best practices for minimizing the occurrence of corneal adverse events and for management of these events when they do occur.

Long-term follow-up and additional analyses are ongoing in the FIGHT trial. The top-line results observed in the FIGHT trial support the advancement of the development of bemarituzumab as a potential treatment for FGFR2b+, non-HER2+ gastric and GEJ cancer. In addition, we believe the results support the potential development of bemarituzumab in other cancers that overexpress FGFR2b, including squamous non-small cell lung cancer, triple negative breast cancer, ovarian cancer, pancreatic cancer and intrahepatic cholangiocarcinoma.

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THE OFFERING

Common stock to be offered by us	7,200,000 shares
Common stock to be outstanding immediately following this offering	42,820,167 shares (or 43,900,167 shares if the underwriters exercise their option to purchase additional shares in full).
Option to purchase additional shares from us	We have granted the underwriters an option for 30 days from the date of this prospectus supplement to purchase up to 1,080,000 additional shares of our common stock.
Use of proceeds	We expect to use the net proceeds from this offering, together with other available funds, (i) to fund ongoing clinical development of bemarituzumab and FPT155, (ii) to advance FPA157 through preclinical and into clinical development, (iii) to advance our late-stage research programs and (iv) for working capital and general corporate purposes. Although we may use a portion of the net proceeds from this offering for the licensing or acquisition of, or the development of, additional product candidates, technologies, compounds, other assets or complementary businesses, we have no current understandings, agreements or commitments to do so. See “Use of Proceeds.”
Risk factors	Investing in our common stock involves a high degree of risk. See “Risk Factors” and other information included in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference in this prospectus supplement and the accompanying prospectus for a discussion of factors you should carefully consider before deciding to invest in shares of our common stock.
Nasdaq Global Select Market symbol	“FPRX”

The number of shares of common stock outstanding immediately following this offering set forth above is based on 35,620,167 shares of common stock outstanding as of September 30, 2020. This number excludes:

• 1,388,433 shares of our common stock sold under our August 6, 2020 sales agreement with Cowen and Company, LLC since September 30, 2020;

• 4,983,628 shares of our common stock issuable upon the exercise of stock options outstanding as of September 30, 2020 under our existing equity incentive plans at a weighted-average exercise price of $14.59 per share;

• 2,305,580 shares of our common stock reserved as of September 30, 2020 for future issuance under our 2013 Omnibus Incentive Plan, or the 2013 Plan, as well as any future increases in the number of shares of our common stock reserved for issuance under the 2013 Plan; and

• 1,254,389 shares of our common stock reserved as of September 30, 2020 for future issuance under our 2013 Employee Stock Purchase Plan, or the ESPP, as well as any future increases in the number of shares of our common stock reserved for issuance under the ESPP.

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RISK FACTORS

An investment in our securities involves a high degree of risk. You should carefully review the risks and uncertainties described below and in the section titled “Risk Factors” in our Quarterly Report on Form 10-Q for the quarter ended September 30, 2020, as updated by our subsequent filings under the Exchange Act, each of which are incorporated by reference into this prospectus supplement in their entirety, together with all of the other information contained in or incorporated by reference into this prospectus supplement, the accompanying prospectus and any free writing prospectus that we have authorized for use in connection with this offering, before deciding whether to purchase any of the securities being registered pursuant to the registration statement of which this prospectus supplement and the accompanying prospectus is a part. Each of the risk factors could adversely affect our business, results of operations, financial condition and cash flows, as well as adversely affect the value of an investment in our securities, and the occurrence of any of these risks might cause you to lose all or part of your investment. Additional risks not presently known to us or that we currently believe are immaterial may also significantly impair our business operations. Please also carefully read the section below titled “Special Note Regarding Forward-Looking Statements.”

Risks Related to this Offering

We have broad discretion in the use of the net proceeds from this offering and may not use them effectively.

Our management will have broad discretion in the application of the net proceeds from this offering, and you will be relying on the judgment of our management regarding the application of these proceeds. You will not have the opportunity, as part of your investment decision, to assess whether we are using the proceeds appropriately. We expect to use the net proceeds from this offering, together with other available funds, (i) to fund ongoing clinical development of bemarituzumab and FPT155, (ii) to advance FPA157 through preclinical and into clinical development, (iii) to advance our late-stage research programs and (iv) for working capital and general corporate purposes. Although we may use a portion of the net proceeds from this offering for the licensing or acquisition of, or the development of, additional product candidates, technologies, compounds, other assets or complementary businesses, we have no current understandings, agreements or commitments to do so. However, our use of these net proceeds may differ substantially from our current plans and our management might not apply our net proceeds in ways that ultimately increase the value of your investment. If we do not invest or apply the net proceeds from this offering in ways that enhance stockholder value, we may fail to achieve expected financial results, which could cause our stock price to decline.

If you purchase our common stock in this offering, you will experience immediate and substantial dilution in investment. You will experience further dilution if we issue additional equity securities in future fundraising transactions.

Since the public offering price per share of our common stock is substantially higher than the net tangible book value per share of our common stock, you will suffer immediate and substantial dilution in the net tangible book value of the common stock you purchase in this offering. As a result, investors purchasing shares of common stock in this offering will incur immediate dilution of approximately $15.46 per share, based upon the public offering price of $21.00 per share, and our net tangible book value as of September 30, 2020, after giving effect to this offering. See the section titled “Dilution” below for a more detailed discussion of the dilution you will incur if you purchase common stock in this offering.

Sales of a substantial amount of shares of our common stock in the public market, particularly sales by our directors, executive officers and significant stockholders, or the perception that these sales could occur, could cause the market price of our common stock to decline and may make it more difficult for you to sell your common stock at a time and price that you deem appropriate. In addition, we have a significant number of shares reserved for issuance in connection upon vesting or exercise of outstanding awards under our equity compensation plans. To the extent that these awards vest or are exercised, investors purchasing our common stock in this offering may experience further dilution. In addition, we may choose to raise additional capital due

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to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent that additional capital is raised through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our stockholders or result in downward pressure on the price of our common stock.

Our executive officers and directors have entered into lock-up agreements with us under which we and they have agreed, subject to specific exceptions described in the section titled “Underwriting,” not to sell, directly or indirectly, any shares of common stock without the permission of the underwriters for a period of 90 days following the date of this prospectus supplement. We refer to such period as the lock-up period. When the lock-up period expires, we and our executive officers and directors will be able to sell our shares in the public market. In addition, the underwriters may, in their sole discretion, release all or some portion of the shares subject to lock-up agreements at any time and for any reason. Sales of a substantial number of such shares upon expiration of the lock-up, the perception that such sales may occur, or early release of these agreements, could cause our market price to fall or make it more difficult for you to sell your common stock at a time and price that you deem appropriate.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement and the accompanying prospectus, including the documents incorporated by reference herein and therein, and any free writing prospectus that we have authorized for use in connection with this offering, contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. These statements are based on our management’s current beliefs, expectations and assumptions about future events, conditions and results and on information currently available to us. Discussions containing these forward-looking statements may be found, among other places, in the sections titled “Business,” “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” incorporated by reference from our most recent Annual Report on Form 10-K and our most recent Quarterly Report on Form 10-Q filed with the SEC, as well as any amendments thereto reflected in subsequent filings with the SEC.

Any statements in this prospectus supplement or the accompanying prospectus, or incorporated by reference herein or therein, and any free writing prospectus, about our expectations, beliefs, plans, objectives, assumptions or future events or performance are not historical facts and are forward-looking statements. Within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act, these forward-looking statements include statements regarding:

• the impact of the COVID-19 pandemic and its effects on our operations, research and development and clinical trials and potential disruption in the operations and business of third-party manufacturers, contract research organizations, other service providers, and collaborators with whom we conduct business;

• our estimates regarding our expenses, revenues, anticipated capital requirements and our needs for additional financing;

• our receipt of future milestone payments and/or royalties, and the timing of such payments;

• our or our partners’ ability to timely advance product candidates into and through clinical data readouts and successful completion of clinical trials;

• the timing of the initiation, progress and results of preclinical studies and research and development programs;

• our expectations regarding the potential safety, efficacy or clinical utility of our product candidates;

• the implementation, timing and likelihood of success of our plans to develop companion diagnostics for our product candidates;

• our ability to establish and maintain collaborations and necessary licenses;

• the implementation of our business model and strategic plans for our business, product candidates and technology;

• the scope of protection we establish and maintain for intellectual property rights covering our product candidates and technology;

• the size of patient populations targeted by products we or our partners develop and market adoption of such products by physicians and patients;

• the extent of protein overexpression or gene amplification in certain patient populations;

• the timing or likelihood of regulatory filings and approvals for products we or our partners develop;

• the ability to negotiate adequate pricing, coverage and adequate reimbursement for our product candidates with third parties and government authorities;

• developments relating to our competitors and our industry;

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• our expectations regarding licensing, acquisitions and strategic operations;

• our anticipated use of proceeds from this offering; and

• political, social and economic instability, natural disasters or public health epidemics in countries where we or our collaborators do business.

In some cases, you can identify forward-looking statements by terminology such as “anticipate,” “believe,” “continue,” “could,” “estimate,” “expects,” “intend,” “may,” “might,” “plan,” “potential,” “predict,” “project,” “should,” “will,” “would” or the negative or plural of those terms, and similar expressions intended to identify statements about the future, although not all forward-looking statements contain these words. These statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from the information expressed or implied by these forward-looking statements. In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this prospectus, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and investors are cautioned not to unduly rely upon these statements.

You should refer to the risks and uncertainties described in the “Risk Factors” section contained in this prospectus supplement, the accompanying prospectus and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus supplement and the accompanying prospectus, for a discussion of important factors that may cause our actual results to differ materially from those expressed or implied by our forward-looking statements. Given these risks, uncertainties and other factors, many of which are beyond our control, we cannot assure you that the forward-looking statements in this prospectus supplement and the accompanying prospectus will prove to be accurate, and you should not place undue reliance on these forward-looking statements. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame, or at all.

Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to revise any forward-looking statements to reflect events or developments occurring after the date of this prospectus supplement, even if new information becomes available in the future.

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USE OF PROCEEDS

We expect to receive approximately $141.9 million in net proceeds from the sale of 7,200,000 shares of common stock offered by us in this offering (approximately $163.2 million if the underwriters exercise their option to purchase 1,080,000 additional shares in full) after deducting underwriting discounts and commissions and estimated offering expenses payable by us.

We expect to use the net proceeds from this offering, together with other available funds, (i) to fund ongoing clinical development of bemarituzumab and FPT155, (ii) to advance FPA157 through preclinical and into clinical development, (iii) to advance our late-stage research programs and (iv) for working capital and general corporate purposes.

The expected use of the net proceeds from this offering represents our intentions based upon our current plans and business conditions, which could change in the future as our plans and business conditions evolve. The amounts and timing of our actual expenditures depend on numerous factors, including the progress of our preclinical development efforts, the ongoing status of and results from our clinical trials and other studies and any unforeseen cash needs. As a result, our management will have broad discretion in applying the net proceeds from this offering. Although we may use a portion of the net proceeds from this offering for the licensing or acquisition of, or the development of, additional product candidates, technologies, compounds, other assets or complementary businesses, we have no current understandings, agreements or commitments to do so. Pending their ultimate use, we intend to invest the net proceeds from this offering in interest-bearing, investment-grade securities.

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DIVIDEND POLICY

We have never declared or paid any cash dividends on our capital stock and do not anticipate paying any cash dividends in the foreseeable future. Payment of cash dividends, if any, in the future will be at the discretion of our board of directors and will depend on then-existing conditions, including our financial condition, operating results, contractual restrictions, capital requirements, business prospects and other factors our board of directors may deem relevant.

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DILUTION

If you invest in our common stock in this offering, your ownership interest will be immediately diluted to the extent of the difference between the public offering price per share of our common stock and the as adjusted net tangible book value per share of our common stock immediately after this offering. Net tangible book value per share of our common stock is determined at any date by subtracting our total liabilities from the amount of our total tangible assets and dividing the difference by the number of shares of our common stock deemed to be outstanding at that date.

Our net tangible book value as of September 30, 2020 was approximately $95.2 million, or $2.67 per share, based on 35,620,167 shares of common stock outstanding as of September 30, 2020. After giving effect to the sale of 7,200,000 shares of common stock in this offering at the public offering price of $21.00 per share, after deducting underwriting discounts and commissions and estimated offering expenses payable by us, our as adjusted net tangible book value as of September 30, 2020 would have been $237.1 million, or $5.54 per share. This amount represents an immediate increase in net tangible book value of $2.87 per share of our common stock to existing stockholders and an immediate dilution in net tangible book value of $15.46 per share of our common stock to new investors purchasing shares of common stock in this offering.

The following table illustrates this dilution on a per share basis to new investors:

Public offering price per share			$	21.00
Net tangible book value per share as of September 30, 2020	$	2.67
Increase in net tangible book value per share attributable to new investors		2.87
As adjusted net tangible book value per share after this offering				5.54
Dilution per share to new investors purchasing common stock in this offering			$	15.46

The information above assumes that the underwriters do not exercise their option to purchase additional shares. If the underwriters exercise their option in full at the public offering price of $21.00, our as adjusted net tangible book value per share as of September 30, 2020 after giving effect to this offering would have been $5.89 per share, and the dilution in as adjusted net tangible book value per share to investors in this offering would have been $15.11 per share.

The number of shares of common stock to be outstanding after this offering is based on 35,620,167 shares of common stock outstanding as of September 30, 2020, and excludes:

• 1,388,433 shares of our common stock sold pursuant to the August 6, 2020 sales agreement with Cowen and Company, LLC since September 30, 2020;

• The number of shares of common stock outstanding immediately following this offering is based on 35,620,167 shares of common stock outstanding as of September 30, 2020. This number excludes: 4,983,628 shares of our common stock issuable upon the exercise of stock options outstanding as of September 30, 2020 under our existing equity incentive plans at a weighted-average exercise price of $14.59 per share;

• 2,305,580 shares of our common stock reserved as of September 30, 2020 for future issuance under the 2013 Plan, as well as any future increases in the number of shares of our common stock reserved for issuance under the 2013 Plan; and

• 1,254,389 shares of our common stock reserved as of September 30, 2020 for future issuance under the ESPP, as well as any future increases in the number of shares of our common stock reserved for issuance under the ESPP.

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To the extent that options outstanding as of September 30, 2020 have been or may be exercised or we issue additional options or shares of our common stock, investors purchasing our common stock in this offering may experience further dilution. In addition, we may choose to raise additional capital due to market conditions or strategic considerations even if we believe we have sufficient funds for our current or future operating plans. To the extent that we raise additional capital through the sale of equity or convertible debt securities, the issuance of these securities could result in further dilution to our stockholders.

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MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES TO NON-U.S. HOLDERS

The following is a discussion of the material U.S. federal income tax consequences applicable to non-U.S. holders (as defined below) with respect to their purchase, ownership and disposition of shares of our common stock issued pursuant to this offering, but does not purport to be a complete analysis of all potential tax effects. All prospective non-U.S. holders of our common stock should consult their tax advisors with respect to the U.S. federal income tax consequences of the purchase, ownership and disposition of our common stock, as well as any consequences arising under the laws of any other taxing jurisdiction, including any state, local and non-U.S. tax consequences and any U.S. federal non-income tax consequences. In general, a non-U.S. holder means a beneficial owner of our common stock (other than a partnership or an entity or arrangement treated as a partnership for U.S. federal income tax purposes) that is not a U.S. holder. A U.S. holder is, for U.S. federal income tax purposes:

• an individual who is a citizen or resident of the United States;

• a corporation, or an entity treated as a corporation for U.S. federal income tax purposes, created or organized in the United States or under the laws of the United States or of any state thereof or the District of Columbia;

• an estate, the income of which is subject to U.S. federal income tax regardless of its source; or

• a trust if (1) a U.S. court can exercise primary supervision over the trust’s administration and one or more U.S. persons have the authority to control all of the trust’s substantial decisions or (2) the trust has a valid election in effect under applicable U.S. Treasury Regulations to be treated as a U.S. person.

This discussion is based on current provisions of the U.S. Internal Revenue Code of 1986, as amended, which we refer to as the Code, existing U.S. Treasury Regulations promulgated thereunder, published administrative rulings and judicial decisions, all as in effect as of the date of this prospectus supplement. These laws are subject to change and to differing interpretation, possibly with retroactive effect. Any change or differing interpretation could alter the tax consequences to non-U.S. holders described in this prospectus supplement.

This discussion is limited to non-U.S. holders that hold shares of our common stock as a capital asset within the meaning of Section 1221 of the Code (generally, for investment). This discussion does not address all aspects of U.S. federal income taxation that may be relevant to a particular non-U.S. holder in light of that non-U.S. holder’s individual circumstances, nor does it address certain special tax rules applicable to particular non-U.S. holders, such as holders that own, or are deemed to own, more than 5% of our capital stock (except to the extent specifically set forth below), corporations that accumulate earnings to avoid U.S. federal income tax, tax-exempt organizations, banks, financial institutions, insurance companies, brokers, dealers or traders in securities, commodities or currencies, tax-qualified retirement plans, holders who hold or receive our common stock pursuant to the exercise of employee stock options or otherwise as compensation, holders holding our common stock as part of a hedge, straddle or other risk reduction strategy, conversion transaction or other integrated investment, holders deemed to sell our common stock under the constructive sale provisions of the Code, “qualified foreign pension funds” as defined in Section 897(l)(2) of the Code and entities all of the interests of which are held by qualified foreign pension funds, controlled foreign corporations, passive foreign investment companies and certain former citizens or long-term residents of the United States. This discussion also does not address the effect of the alternative minimum tax or the Medicare contribution tax on net investment income, the impact of special tax accounting rules under Section 451(b) of the Code, any aspects of U.S. estate or gift tax, or any state, local or non-U.S. taxes.

In addition, this discussion does not address the tax treatment of partnerships (or entities or arrangements that are treated as partnerships for U.S. federal income tax purposes) or persons that hold our common stock through such partnerships, entities or arrangements. If a partnership, including any entity or arrangement treated as a partnership for U.S. federal income tax purposes, holds shares of our common stock, the U.S. federal income tax treatment of a partner in such partnership will generally depend upon the status of the partner, the activities of the

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partnership and certain determinations made at the partner level. Such partners and partnerships should consult their tax advisors regarding the tax consequences of the purchase, ownership and disposition of our common stock.

There can be no assurance that the U.S. Internal Revenue Service, which we refer to as the IRS, will not challenge one or more of the tax consequences described herein, and we have not obtained, nor do we intend to obtain, a ruling from the IRS regarding the U.S. federal income tax consequences with respect to the matters discussed below.

Distributions on Our Common Stock

As described in the section entitled “Dividend Policy,” we do not anticipate declaring or paying dividends to holders of our common stock in the foreseeable future. However, distributions, if any, on our common stock generally will constitute dividends for U.S. federal income tax purposes to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. If a distribution exceeds our current and accumulated earnings and profits, the excess will be treated as a tax-free return of the non-U.S. holder’s investment, up to such holder’s adjusted tax basis in the common stock. Any remaining excess will be treated as capital gain from the sale or exchange of such common stock, subject to the tax treatment described below in “Gain on Sale, Exchange or Other Disposition of Our Common Stock.”

Subject to the discussions below regarding effectively connected income, dividends paid to a non-U.S. holder generally will be subject to withholding of U.S. federal income tax at a 30% rate, or such lower rate as may be specified by an applicable income tax treaty. A non-U.S. holder that is eligible for a reduced rate of U.S. withholding tax under an income tax treaty may obtain a refund or credit of any excess amounts withheld by timely filing an appropriate claim for refund with the IRS. A non-U.S. holder of our common stock who claims the benefit of an applicable income tax treaty generally will be required to provide a properly executed IRS Form W-8BEN or W-8BEN-E (or successor form) and satisfy relevant certification and other requirements. Non-U.S. holders are urged to consult their tax advisors regarding their entitlement to benefits under a relevant income tax treaty.

Dividends that are treated as effectively connected with a trade or business conducted by a non-U.S. holder within the United States and, if an applicable income tax treaty so provides, that are attributable to a permanent establishment or a fixed base maintained by the non-U.S. holder within the United States, generally are exempt from the 30% withholding tax if the non-U.S. holder satisfies applicable certification requirements. To claim the exemption, the non-U.S. holder must furnish to us or the applicable withholding agent a valid IRS Form W-8ECI (or applicable successor form), certifying that the dividends are effectively connected with the non-U.S. holder’s conduct of a trade or business within the United States. However, such U.S. effectively connected income, net of specified deductions and credits, is taxed at the U.S. federal income tax rates applicable to a “United States person” (as defined in the Code), which we refer to as a United States person, unless a specific treaty exemption applies. Any U.S. effectively connected income received by a non-U.S. holder that is a corporation may also, under certain circumstances, be subject to an additional “branch profits tax” at a 30% rate or such lower rate as may be specified by an applicable income tax treaty.

Gain on Sale, Exchange or Other Disposition of Our Common Stock

Subject to the discussions below regarding backup withholding and foreign accounts, in general, a non-U.S. holder will not be subject to any U.S. federal income tax on any gain realized upon such holder’s sale, exchange or other disposition of shares of our common stock unless:

• the gain is effectively connected with a U.S. trade or business of the non-U.S. holder and, if an applicable income tax treaty so provides, is attributable to a permanent establishment or a fixed base maintained in the United States by such non-U.S. holder, in which case the non-U.S. holder generally

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will be taxed at the U.S. federal income tax rates applicable to United States persons and, if the non-U.S. holder is a foreign corporation, the branch profits tax described above in “Distributions on Our Common Stock” also may apply;

• the non-U.S. holder is a nonresident alien individual who is present in the United States for 183 days or more in the taxable year of the disposition and certain other conditions are met, in which case the non-U.S. holder will be subject to a 30% tax (or such lower rate as may be specified by an applicable income tax treaty) on the net gain derived from the disposition, which may be offset by certain U.S. source capital losses of the non-U.S. holder, if any (even though the individual is not considered a resident of the United States), provided the non-U.S. holder has timely filed U.S. federal income tax returns with respect to such losses; or

• our common stock constitutes a U.S. real property interest because we are, or have been, at any time during the five-year period preceding such disposition (or the non-U.S. holder’s holding period, if shorter) a “United States real property holding corporation.” Even if we are or become a United States real property holding corporation, provided that our common stock is “regularly traded” (as defined by U.S. Treasury Regulations) on an established securities market, our common stock will be treated as a U.S. real property interest only with respect to a non-U.S. holder that holds more than 5% of our outstanding common stock, directly or indirectly, actually or constructively, during the shorter of the five-year period ending on the date of the disposition or the period that the non-U.S. holder held our common stock. In such case, such non-U.S. holder generally will be taxed on its net gain derived from the disposition at the U.S. federal income tax rates applicable to United States persons. Generally, a corporation is a United States real property holding corporation only if the fair market value of its U.S. real property interests equals or exceeds 50% of the sum of (i) the fair market value of its worldwide real property interests and (ii) its other assets used or held for use in a trade or business. Although there can be no assurance, we do not believe that we are, or have been, a United States real property holding corporation, or that we are likely to become one in the future. No assurance can be provided that our common stock will be regularly traded on an established securities market for purposes of the rules described above.

Backup Withholding and Information Reporting

We must report annually to the IRS and to each non-U.S. holder the gross amount of distributions on our common stock paid to such holder, regardless of whether such distributions constitute dividends or whether any tax was withheld. A non-U.S. holder will have to comply with specific certification procedures to establish that it is not a United States person in order to avoid backup withholding at the applicable rate with respect to dividends on our common stock. U.S. backup withholding generally will not apply to a non-U.S. holder who provides a properly executed IRS Form W-8BEN or W-8BEN-E (or successor form) or otherwise establishes an exemption.

Information reporting and backup withholding generally will apply to the proceeds of a disposition of our common stock by a non-U.S. holder effected by or through the U.S. office of any broker, U.S. or foreign, unless the holder certifies its status as a non-U.S. holder and satisfies certain other requirements, or otherwise establishes an exemption. Generally, information reporting and backup withholding will not apply to a payment of disposition proceeds to a non-U.S. holder where the transaction is effected outside the United States through a non-U.S. office of a broker. However, for information reporting purposes, dispositions effected through a non-U.S. office of a broker with substantial U.S. ownership or operations generally will be treated in a manner similar to dispositions effected through a U.S. office of a broker.

Non-U.S. holders should consult their tax advisors regarding the application of the information reporting and backup withholding rules to them.

Copies of information returns may be made available to the tax authorities of the country in which the non-U.S. holder resides or is incorporated under the provisions of a specific treaty or agreement.

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Backup withholding is not an additional tax. Any amounts withheld under the backup withholding rules from a payment to a non-U.S. holder may be allowed as a credit against the non-U.S. holder’s U.S. federal income tax liability, if any, and may entitle such holder to a refund, provided that the required information is timely furnished to the IRS.

Foreign Accounts

Sections 1471 through 1474 of the Code (commonly referred to as FATCA) generally impose a U.S. federal withholding tax of 30% on certain payments made to a “foreign financial institution” (as specifically defined for this purpose), unless such institution enters into an agreement with the U.S. government to, among other things, withhold on certain payments and collect and provide to the U.S. tax authorities substantial information regarding U.S. account holders of such institution (which may include certain equity and debt holders of such institution, as well as certain account holders that are foreign entities with U.S. owners). Foreign financial institutions located in jurisdictions that have an intergovernmental agreement with the United States governing these withholding and reporting requirements may be subject to different rules. FATCA also generally imposes a 30% withholding tax on certain payments made to a non-financial foreign entity, unless such entity provides the withholding agent with either a certification that it does not have any substantial direct or indirect U.S. owners, or information regarding substantial direct and indirect U.S. owners of the entity. The withholding tax under FATCA described above will not apply if the foreign financial institution or non-financial foreign entity otherwise qualifies for an exemption from the rules. The FATCA withholding provisions described above currently apply to dividends on our common stock. The FATCA withholding provisions also would apply to the gross proceeds of a disposition of our common stock, except that the U.S. Treasury Department has released proposed regulations which, if finalized in their present form, would eliminate such withholding. In its preamble to such proposed regulations, the U.S. Treasury Department stated that taxpayers generally may rely on the proposed regulations until final regulations are issued.

Under certain circumstances, a non-U.S. holder might be eligible for refunds or credits of such taxes. Non-U.S. holders are encouraged to consult with their tax advisors regarding the possible implications of FATCA on their investment in our common stock.

EACH PROSPECTIVE INVESTOR SHOULD CONSULT ITS TAX ADVISORS REGARDING THE TAX CONSEQUENCES OF PURCHASING, HOLDING AND DISPOSING OF OUR COMMON STOCK, AS WELL AS TAX CONSEQUENCES ARISING UNDER ANY STATE, LOCAL, NON-U.S. OR U.S. FEDERAL NON-INCOME TAX LAWS.

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UNDERWRITING

We are offering the shares of common stock described in this prospectus supplement through the several underwriters named in the table below. Cowen and Company, LLC and SVB Leerink LLC are acting as representatives of the several underwriters listed below. We have entered into an underwriting agreement with the underwriters. Subject to the terms and conditions of the underwriting agreement, we have agreed to sell to the underwriters, and each underwriter has severally agreed to purchase, at the public offering price less the underwriting discounts and commissions set forth on the cover page of this prospectus supplement, the number of shares of common stock listed next to its name in the following table:

Name	Number of Shares
Cowen and Company, LLC		3,060,000
SVB Leerink LLC		3,060,000
Wedbush Securities Inc.		1,080,000
Total		7,200,000

The underwriters are committed to purchase all the shares offered by us if they purchase any shares. The underwriting agreement also provides that if an underwriter defaults, the purchase commitments of non-defaulting underwriters may also be increased or the offering may be terminated. We have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act of 1933.

The underwriters propose to offer the shares of our common stock directly to the public at the initial public offering price set forth on the cover page of this prospectus supplement and to certain dealers at that price less a concession not in excess of $0.756 per share. After the initial offering of the shares to the public, the offering price and other selling terms may be changed by the underwriters. The offering of the shares by the underwriters is subject to receipt and acceptance and subject to the underwriters’ right to reject any order in whole or in part.

Option to Purchase Additional Shares

The underwriters have an option to buy up to 1,080,000 additional shares of common stock from us to cover sales of shares by the underwriters which exceed the number of shares specified in the table above. The underwriters have 30 days from the date of this prospectus supplement to exercise this option to purchase additional shares. If any shares are purchased with this option to purchase additional shares, the underwriters will purchase shares in approximately the same proportion as shown in the table above. If any additional shares of common stock are purchased, the underwriters will offer the additional shares on the same terms as those on which the shares are being offered.

Discounts and Commissions

The underwriting fee is equal to the public offering price per share of common stock less the amount paid by the underwriters to us per share of common stock. The underwriting fee is $1.26 per share. The following table shows the per share and total underwriting discounts and commissions to be paid to the underwriters assuming both no exercise and full exercise of the underwriters’ option to purchase additional shares.

	Without option to purchase additional shares exercise		With full option to purchase additional shares exercise
Per share	$	1.26	$	1.26
Total	$	9,072,000	$	10,432,800

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We estimate that our total expenses of this offering, excluding the underwriting discounts and commissions and the structuring fees, will be approximately $250,000.

A prospectus supplement in electronic format may be made available on the websites maintained by one or more underwriters, or selling group members, if any, participating in the offering. The underwriters may agree to allocate a number of shares to underwriters and selling group members for sale to their online brokerage account holders. Internet distributions will be allocated by the representatives to underwriters and selling group members that may make Internet distributions on the same basis as other allocations.

No Sales of Similar Securities

We have agreed that we will not (i) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise dispose of, directly or indirectly, or submit to, or file with, the SEC a registration statement under the Securities Act relating to, any shares of our common stock or securities convertible into or exchangeable or exercisable for any shares of our common stock, or publicly disclose the intention to undertake any of the foregoing, or (ii) enter into any swap or other agreement that transfers all or a portion of the economic consequences associated with the ownership of any shares of common stock or any such other securities (regardless of whether any of these transactions are to be settled by the delivery of shares of common stock or such other securities, in cash or otherwise), in each case without the prior written consent of the representatives for a period of 90 days after the date of this prospectus supplement. Notwithstanding these restrictions, we may: (A) effect the sale of the shares contemplated by this prospectus supplement; (B) issue shares of our common stock or options to purchase common stock, or issue shares of common stock upon exercise of options, in each case pursuant to any stock option, stock bonus or other stock plan or arrangement described in the registration statement or this prospectus supplement; provided that, if the holder of any such common stock or other securities is a director or executive officer referred to in the paragraph below, any securities acquired will remain subject to the restrictions set forth in the paragraph below; (C) withhold and cancel shares of our common stock released upon vesting of restricted stock awards granted pursuant to any restricted stock agreement, stock bonus or other stock plan or arrangement described in the registration statement or this prospectus supplement in order to pay withholding taxes to tax authorities on behalf of the recipient of any such restricted stock award, and (D) issue (or agree to issue) shares of common stock or related securities (as defined below) in connection with a licensing arrangement, joint venture, acquisition or business combination or other collaboration or strategic transaction; provided that, in the case of clause (D), recipients of such common stock or related securities agree to be bound by the terms of the lock-up described in the paragraph below applicable to our directors and executive officers and the sum of the aggregate number of shares of common stock or related securities so issued shall not exceed 5% of the total outstanding shares of our common stock prior to giving effect to the sale of the shares offered by this prospectus supplement. For purposes of the foregoing, “related securities” shall mean any options or warrants or other rights to acquire common stock or any securities exchangeable or exercisable for or convertible into common stock, or to acquire other securities or rights ultimately exchangeable or exercisable for, or convertible into, our common stock.

Our directors and executive officers have entered into lock-up agreements with the underwriters prior to the commencement of this offering pursuant to which each of these persons, for a period of 90 days after the date of this prospectus supplement, may not, without the prior written consent of the representatives on behalf of the underwriters, (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any shares of our common stock or any securities convertible into or exercisable or exchangeable for our common stock (including, without limitation, common stock or such other securities which may be deemed to be beneficially owned by such directors, executive officers, managers and members in accordance with the rules and regulations of the SEC and securities which may be issued upon exercise of a stock option or warrant) or publicly disclose the intention to make any offer, sale, pledge or disposition, (2) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the common

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stock or such other securities, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of common stock or such other securities, in cash or otherwise, or (3) make any demand for or exercise any right with respect to the registration of any shares of our common stock or any security convertible into or exercisable or exchangeable for our common stock, in each case other than: (A) transfers of shares of our common stock or options or other rights to acquire shares of our common stock as a bona fide gift; (B) distributions of shares of our common stock to members or stockholders of the undersigned; (C) transfers of shares of our common stock or options or other rights to acquire shares of our common stock pursuant to a qualified domestic relations order or a negotiated divorce settlement; and (D) transfer or surrender for cancellation of shares of our common stock to us upon the vesting of restricted shares of common stock to cover tax withholding obligations in connection with such vesting pursuant to a restricted stock agreement, stock bonus or other stock plan or arrangement existing as of the date hereof and described in our public filings with the SEC, and any remaining shares of common stock acquired upon such vesting shall remain subject to the restrictions described in this paragraph; provided that in the case of any transfer or distribution pursuant to clause (A), (B), or (C), each donee or distributee shall execute and deliver to the representatives a lock-up letter in the form of set forth in this paragraph; and provided, further, that in the case of any transfer or distribution pursuant to clause (A), (B) or (C), no filing by any party (donor, donee, transferor or transferee) under the Exchange Act or other public announcement shall be required or shall be made voluntarily in connection with such transfer or distribution (other than a filing on a Form 5 made after the expiration of the 90-day period referred to above unless such Form 5 is required to be filed during such period). In addition, our directors and executive officers may (1) sell shares of our common stock pursuant to a trading plan established pursuant to Rule 10b5-1 under the Exchange Act, or a 10b5-1 plan, existing on the date hereof and disclosed to the representatives and (2) enter into a 10b5-1 plan during the 90 day period; provided that in the case of any sales pursuant to (1), each filing with the SEC shall indicate that the sale was made pursuant to an existing 10b5-1 plan and, in the case of (2), such 10b5-1 plan does not allow for any sales during the 90-day period and no filing under the Exchange Act or other public announcement shall be required or shall be made voluntarily in connection with the establishment of such 10b5-1 plan.

Other Relationships

The underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include sales and trading, commercial and investment banking, advisory, investment management, investment research, principal investment, hedging, market making, brokerage and other financial and non-financial activities and services. Certain of the underwriters and their respective affiliates have provided, and may in the future provide, a variety of these services to us and to persons and entities with relationships with us, for which they received or will receive customary fees and expenses.

In the ordinary course of their various business activities, the underwriters and their respective affiliates, officers, directors and employees may purchase, sell or hold a broad array of investments and actively trade securities, derivatives, loans, commodities, currencies, credit default swaps and other financial instruments for their own account and for the accounts of their customers, and such investment and trading activities may involve or relate to assets, securities and/or instruments of ours (directly, as collateral securing other obligations or otherwise) and/or persons and entities with relationships with us. The underwriters and their respective affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such assets, securities or instruments and may at any time hold, or recommend to clients that they should acquire, long and/or short positions in such assets, securities and instruments.

Stabilization and Short Positions

In connection with this offering, the underwriters may engage in stabilizing transactions, which involves making bids for, purchasing and selling shares of common stock in the open market for the purpose of preventing or retarding a decline in the market price of the common stock while this offering is in progress. These stabilizing

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transactions may include making short sales of the common stock, which involves the sale by the underwriters of a greater number of shares of common stock than they are required to purchase in this offering, and purchasing shares of common stock on the open market to cover positions created by short sales. Short sales may be “covered” shorts, which are short positions in an amount not greater than the underwriters’ option to purchase additional shares referred to above, or may be “naked” shorts, which are short positions in excess of that amount. The underwriters may close out any covered short position either by exercising their option to purchase additional shares, in whole or in part, or by purchasing shares in the open market. In making this determination, the underwriters will consider, among other things, the price of shares available for purchase in the open market compared to the price at which the underwriters may purchase shares through the option to purchase additional shares. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the common stock in the open market that could adversely affect investors who purchase in this offering. To the extent that the underwriters create a naked short position, they will purchase shares in the open market to cover the position.

The underwriters have advised us that, pursuant to Regulation M of the Securities Act of 1933, they may also engage in other activities that stabilize, maintain or otherwise affect the price of the common stock, including the imposition of penalty bids. This means that if the representatives of the underwriters purchase common stock in the open market in stabilizing transactions or to cover short sales, the representatives can require the underwriters that sold those shares as part of this offering to repay the underwriting discount received by them.

These activities may have the effect of raising or maintaining the market price of the common stock or preventing or retarding a decline in the market price of the common stock, and, as a result, the price of the common stock may be higher than the price that otherwise might exist in the open market. If the underwriters commence these activities, they may discontinue them at any time. The underwriters may carry out these transactions on The Nasdaq Global Select Market, in the over-the-counter market or otherwise.

In addition, in connection with this offering certain of the underwriters (and selling group members) may engage in passive market making transactions in our common stock on The Nasdaq Global Select Market prior to the pricing and completion of this offering. Passive market making consists of displaying bids on The Nasdaq Global Select Market no higher than the bid prices of independent market makers and making purchases at prices no higher than these independent bids and effected in response to order flow. Net purchases by a passive market maker on each day are generally limited to a specified percentage of the passive market maker’s average daily trading volume in the common stock during a specified period and must be discontinued when such limit is reached. Passive market making may cause the price of our common stock to be higher than the price that otherwise would exist in the open market in the absence of these transactions. If passive market making is commenced, it may be discontinued at any time.

Selling Restrictions

General

Other than in the United States, no action has been taken by us or the underwriters that would permit a public offering of the securities offered by this prospectus supplement in any jurisdiction where action for that purpose is required. The securities offered by this prospectus supplement may not be offered or sold, directly or indirectly, nor may this prospectus supplement or any other offering material or advertisements in connection with the offer and sale of any such securities be distributed or published in any jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. Persons into whose possession this prospectus supplement comes are advised to inform themselves about and to observe any restrictions relating to the offering and the distribution of this prospectus supplement. This prospectus supplement does not constitute an offer to sell or a solicitation of an offer to buy any securities offered by this prospectus supplement in any jurisdiction in which such an offer or a solicitation is unlawful.

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Notice to Prospective Investors in the European Economic Area and United Kingdom

In relation to each Member State of the European Economic Area and the United Kingdom which has implemented the Prospectus Regulation (each, a “Relevant State”), with effect from and including the date on which the Prospectus Regulation is implemented in that Relevant State, no offer of our shares may be made to the public in that Relevant State other than:

A. to any legal entity which is a qualified investor as defined in the Prospectus Regulation;

B. to fewer than 150 natural or legal persons (other than qualified investors as defined in the Prospectus Regulation), subject to obtaining the prior consent of the underwriters for any such offer; or

C. in any other circumstances falling within Article 3(2) of the Prospectus Regulation,

provided that no such offer of shares shall require the Company or any underwriter to publish a prospectus pursuant to Article 3 of the Prospectus Regulation or supplement a prospectus pursuant to Article 23 of the Prospectus Regulation and each person who initially acquires any shares or to whom any offer is made will be deemed to have represented, acknowledged and agreed to and with each of the underwriters and us that it is a “qualified investor” within the meaning of Article 2(e) of the Prospectus Regulation. In the case of any shares being offered to a financial intermediary as that term is used in the Prospectus Regulation, each such financial intermediary will be deemed to have represented, acknowledged and agreed that the shares acquired by it in the offer have not been acquired on a non-discretionary basis on behalf of, nor have they been acquired with a view to their offer or resale to, persons in circumstances which may give rise to an offer of any shares to the public other than their offer or resale in a Relevant State to qualified investors as so defined or in circumstances in which the prior consent of the representatives has been obtained to each such proposed offer or resale.

For the purposes of this provision, the expression an “offer of shares to the public” in relation to any shares in any Relevant State means the communication in any form and by means of sufficient information on the terms of the offer and the shares to be offered so as to enable an investor to decide to purchase or subscribe for any of our shares, and the expression “Prospectus Regulation” means Regulation (EU) 2017/1129.

Notice to Prospective Investors in the United Kingdom

In addition, in the United Kingdom, this prospectus supplement is being distributed only to, and is directed only at, and any offer subsequently made may only be directed at persons who are “qualified investors” (as defined in the Prospectus Regulation) (i) who have professional experience in matters relating to investments falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005, as amended (the “Order”) and/or (ii) who are high net worth companies (or persons to whom it may otherwise be lawfully communicated) falling within Article 49(2)(a) to (d) of the Order (all such persons together being referred to as “relevant persons”) or otherwise in circumstances which have not resulted and will not result in an offer to the public of the shares in the United Kingdom within the meaning of the Financial Services and Markets Act 2000.

Any person in the United Kingdom that is not a relevant person should not act or rely on the information included in this document or use it as basis for taking any action. In the United Kingdom, any investment or investment activity that this document relates to may be made or taken exclusively by relevant persons. Any person in the United Kingdom that is not a relevant person should not act or rely on this document or any of its contents.

Notice to Prospective Investors in Canada

The shares may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the shares must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

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Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

Notice to Prospective Investors in Hong Kong

The shares have not been offered or sold and will not be offered or sold in Hong Kong by means of any document other than (i) to “professional investors” within the meaning of the Securities and Futures Ordinance (Cap. 571) of Hong Kong and any rules made thereunder, or (ii) in other circumstances which do not result in the document being a “prospectus” as defined in the Companies (Winding Up and Miscellaneous Provisions) Ordinance (Cap. 32) of Hong Kong or which do not constitute an offer to the public within the meaning of that Ordinance. No advertisement, invitation or document relating to the shares has been or may be issued or has been or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public in Hong Kong (except if permitted to do so under the securities laws of Hong Kong) other than with respect to shares which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” within the meaning of the Securities and Futures Ordinance and any rules made thereunder.

Notice to Prospective Investors in Singapore

Singapore SFA Product Classification—In connection with Section 309B of the SFA and the CMP Regulations 2018, unless otherwise specified before an offer of shares, we have determined, and hereby notify all relevant persons (as defined in Section 309A(1) of the SFA), that the shares are “prescribed capital markets products” (as defined in the CMP Regulations 2018) and Excluded Investment Products (as defined in MAS Notice SFA 04-N12: Notice on the Sale of Investment Products and MAS Notice FAA-N16: Notice on Recommendations on Investment Products).

Neither this prospectus supplement nor the accompanying prospectus has been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, neither this prospectus supplement, the accompanying prospectus nor any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares may not be circulated or distributed, nor may the shares be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than: (i) to an institutional investor under (as defined in Section 4A of the Securities and Futures Act (Chapter 289) of Singapore, as modified or amended from time to time, or the SFA) pursuant to Section 274 of the SFA; (ii) to a relevant person (as defined in Section 275(2) of the SFA) pursuant to Section 275(1) of the SFA in accordance with the conditions specified in Section 275 of the SFA); or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the shares are subscribed or purchased under Section 275 by a relevant person which is: (a) a corporation (which is not an accredited investor (as defined in Section 4A of the SFA)) the sole business of which is to hold investments and the entire share capital of which is owned by one or more individuals, each of whom is an accredited investor; or (b) a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary of the trust is an individual who is an accredited investor, securities or securities-based derivatives contracts (each term as defined in Section 2(1) of the SFA) of that corporation or the beneficiaries’ rights and interest (howsoever described) in that trust shall not be transferred within six months

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after that corporation or that trust has acquired the shares pursuant to an offer made under Section 275 of the SFA except: (1) to an institutional investor or to a relevant person, or to any person arising from an offer referred to in Section 276(4)(i)(B) of the SFA; (2) where no consideration is or will be given for the transfer; (3) where the transfer is by operation of law; (4) as specified in Section 276(7) of the SFA; or (5) as specified in Regulation 37A of the Securities and Futures (Offers of Investments) (Securities and Securities-based Derivatives Contracts) Regulations 2018.

Notice to Prospective Investors in Japan

The securities have not been and will not be registered pursuant to Article 4, Paragraph 1 of the Financial Instruments and Exchange Act. Accordingly, none of the shares nor any interest therein may be offered or sold, directly or indirectly, in Japan or to, or for the benefit of, any “resident” of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to or for the benefit of a resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the Financial Instruments and Exchange Act and any other applicable laws, regulations and ministerial guidelines of Japan in effect at the relevant time.

Notice to Prospective Investors in Israel

In the State of Israel this prospectus shall not be regarded as an offer to the public to purchase shares of our common stock under the Israeli Securities Law, 5728 - 1968, which requires a prospectus to be published and authorized by the Israel Securities Authority, if it complies with certain provisions of Section 15 of the Israeli Securities Law, 5728-1968, including, inter alia, if: (i) the offer is made, distributed or directed to not more than 35 investors, subject to certain conditions, or the Addressed Investors; or (ii) the offer is made, distributed or directed to certain qualified investors defined in the First Addendum of the Israeli Securities Law, 5728 - 1968, subject to certain conditions, or the Qualified Investors. The Qualified Investors shall not be taken into account in the count of the Addressed Investors and may be offered to purchase securities in addition to the 35 Addressed Investors. We have not and will not take any action that would require us to publish a prospectus in accordance with and subject to the Israeli Securities Law, 5728 - 1968. We have not and will not distribute this prospectus or make, distribute or direct an offer to subscribe for our common stock to any person within the State of Israel, other than to Qualified Investors and up to 35 Addressed Investors.

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LEGAL MATTERS

Certain legal matters relating to the issuance of the shares offered by this prospectus supplement will be passed upon for us by Cooley LLP, Palo Alto, California. Davis Polk & Wardwell LLP, Menlo Park, California, is counsel to the underwriters in connection with this offering.

EXPERTS

Ernst & Young LLP, an independent registered public accounting firm, has audited our financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2019, and the effectiveness of our internal control over financial reporting as of December 31, 2019, as set forth in their reports, which are incorporated by reference in this prospectus supplement. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus supplement is part of a registration statement we filed with the SEC and does not contain all of the information set forth in the registration statement and the exhibits to the registration statement. The rules and regulations of the SEC allow us to omit from this prospectus supplement and the accompanying prospectus certain information included in the registration statement. For further information with respect to us and the securities we are offering under this prospectus supplement, we refer you to the registration statement and the exhibits and schedules filed as a part of the registration statement. We have not, and the underwriters have not, authorized anyone to provide any information other than that contained in or incorporated by reference in this prospectus supplement, the accompanying prospectus and any free writing prospectus prepared by or on behalf of us or to which we have referred you. We take, and the underwriters take, no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We are offering to sell, and seeking offers to buy, shares of our common stock only in jurisdictions where such offers and sales are permitted. You should assume that the information appearing in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein and therein, and in any free writing prospectus that we have authorized for use in connection with this offering, is accurate only as of the dates of those respective documents, regardless of the time of delivery of such documents or of any sale of shares of our common stock.

We file annual, quarterly and current reports, proxy statements and other information with the SEC. The SEC maintains a website that contains reports, proxy and information statements and other information regarding issuers that file electronically with the SEC, including Five Prime. The address of the SEC website is www.sec.gov.

We maintain a website at www.fiveprime.com. Information contained in or accessible through our website does not constitute a part of this prospectus supplement or accompanying prospectus and will not be deemed to be incorporated by reference herein or therein.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information into this prospectus supplement and the accompanying prospectus, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The SEC file number for the documents incorporated by reference in this prospectus supplement is 001-36070. The documents incorporated by reference into this prospectus supplement and the accompanying prospectus contain important information that you should read about us.

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The following documents are incorporated by reference into this document:

• our Annual Report on Form 10-K for the year ended December 31, 2019, which was filed with the SEC on February 27, 2020;

• the information specifically incorporated by reference into our Annual Report on Form 10-K for the year ended December 31, 2019 from our definitive proxy statement relating to our 2020 annual meeting of stockholders, which was filed with the SEC on April 3, 2020;

• our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2020, June 30, 2020 and September 30, 2020, which were filed with the SEC on May  7, 2020, August  6, 2020 and November 3, 2020, respectively;

• our Current Reports on Form 8-K, which were filed with the SEC on January 21, 2020, February 18, 2020, February 26, 2020, April 14, 2020, April 17, 2020, May  20, 2020, August  6, 2020 (other than Item 2.01 and Exhibit 99.1), September  1, 2020, September  4, 2020, November  2, 2020 and November 10, 2020, and our Current Report on Form 8-K/A, which was filed with the SEC on April 6, 2020; and

• the description of our common stock contained in our registration statement on Form 8-A, which was filed with the SEC on September 16, 2013, including any amendments or reports filed for the purpose of updating the description.

We also incorporate by reference into this prospectus supplement and the accompanying prospectus all documents (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (i) after the date of the initial filing of the registration statement of which this prospectus supplement forms a part and prior to effectiveness of the registration statement, or (ii) after the date of this prospectus supplement but prior to the termination of the offering. These documents include periodic reports, such as Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, as well as proxy statements.

Any statement contained in a document incorporated by reference in this prospectus supplement shall be deemed to be modified or superseded for purposes of this prospectus supplement to the extent that a statement contained in this prospectus supplement or in any other subsequently filed document that also is or is deemed to be incorporated by reference in this prospectus supplement modifies or supersedes such statement. Any statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement.

You may obtain copies of any of these filings by contacting us at the address and telephone number indicated below or by contacting the SEC as described above in the section titled “Where You Can Find More Information.” Documents incorporated by reference are available from us without charge, excluding all exhibits unless an exhibit has been specifically incorporated by reference into this prospectus supplement, by requesting them in writing or by telephone at:

Five Prime Therapeutics, Inc.

Attention: Investor Relations

111 Oyster Point Boulevard

South San Francisco, California 94080

(415) 365-5737

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PROSPECTUS

$250,000,000

Common Stock

From time to time, we may offer and sell up to an aggregate amount of $250,000,000 of shares of our common stock in one or more offerings.

We will provide specific terms of these offerings in one or more supplements to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectus may also add, update or change information contained in this prospectus. You should carefully read this prospectus, the applicable prospectus supplement and any related free writing prospectus, as well as any documents incorporated by reference, before you invest in any of the shares of common stock being offered.

This prospectus may not be used to consummate a sale of our common stock unless accompanied by a prospectus supplement.

Our common stock is listed on The Nasdaq Global Select Market, or Nasdaq, under the symbol “FPRX.” On November 2, 2018, the last reported sale price of our common stock was $12.83 per share. The applicable prospectus supplement will contain information, where applicable, as to any other listing on Nasdaq or any securities market or other exchange of the shares of common stock, if any, covered by the prospectus supplement.

We will sell shares of our common stock directly to investors, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. For additional information on the methods of sale, you should refer to the section titled “Plan of Distribution” in this prospectus. If any agents or underwriters are involved in the sale of any shares of our common stock with respect to which this prospectus is being delivered, the names of such agents or underwriters and any applicable fees, commissions, discounts or over-allotment options will be set forth in a prospectus supplement. The price to the public of such shares of our common stock and the net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.

Investing in shares of our common stock involves a high degree of risk. You should review carefully the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus and under similar headings in the other documents that are incorporated by reference into this prospectus as described on page 3 of this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is August 22, 2019.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS	ii
PROSPECTUS SUMMARY	1
RISK FACTORS	3
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	4
USE OF PROCEEDS	6
DESCRIPTION OF CAPITAL STOCK	7
PLAN OF DISTRIBUTION	11
LEGAL MATTERS	13
EXPERTS	13
WHERE YOU CAN FIND MORE INFORMATION	13
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE	13

ABOUT THIS PROSPECTUS

This prospectus is a part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may, from time to time, offer and sell in one or more offerings up to a total dollar amount of $250,000,000 of shares of our common stock, as described in this prospectus.

Each time we offer shares of our common stock under this prospectus, we will provide a prospectus supplement that will contain specific information about the terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change information contained in this prospectus or in any documents that we have incorporated by reference into this prospectus. You should read this prospectus, any applicable prospectus supplement and any related free writing prospectus, together with the information incorporated herein by reference as described under the heading “Incorporation of Certain Information by Reference,” before investing in any of the shares of our common stock offered.

This prospectus may not be used to consummate a sale of shares of our common stock unless it is accompanied by a prospectus supplement.

You should rely only on the information contained in, or incorporated by reference into, this prospectus and any applicable prospectus supplement, along with the information contained in any free writing prospectuses we have authorized for use in connection with a specific offering. We have not authorized anyone to provide you with any information other than that contained or incorporated by reference in this prospectus and any applicable prospectus supplement, along with the information contained in any free writing prospectuses we have authorized for use in connection with a specific offering. You must not rely upon any information or representation that is not contained or incorporated by reference in this prospectus, the accompanying prospectus supplement or in any related free writing prospectus that we may authorize to be provided to you. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. This prospectus is an offer to sell only the shares of our common stock offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so.

The information appearing in this prospectus, any applicable prospectus supplement or any related free writing prospectus is accurate only as of the date on the front of the document, and any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus, any applicable prospectus supplement or any related free writing prospectus, or any sale of shares of our common stock. Our business, financial condition, results of operations and prospects may have changed since those dates.

This prospectus contains and incorporates by reference market data and industry statistics and forecasts that are based on independent industry publications and other publicly available information. Although we believe that these sources are reliable, we do not guarantee the accuracy or completeness of this information and we have not independently verified this information. Although we are not aware of any misstatements regarding the market and industry data presented in this prospectus or the documents incorporated herein by reference, these estimates involve risks and uncertainties and are subject to change based on various factors, including those discussed under the section titled “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus. Accordingly, investors should not place undue reliance on this information.

This prospectus and the information incorporated herein by reference contains summaries of certain provisions contained in some of the documents described herein, but you should refer to the actual documents for complete information. All the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits

ii

to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the heading “Where You Can Find More Information.”

Unless the context indicates otherwise, references in this prospectus to “Five Prime,” “the Company,” “we,” “us,” “our” and similar references refer to Five Prime Therapeutics, Inc. The Five Prime logo is our registered trademark. This prospectus also contains registered marks, trademarks and trade names of other companies. All other trademarks, registered marks and trade names appearing in this prospectus are the property of their respective holders.

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PROSPECTUS SUMMARY

The following summary highlights information contained elsewhere in this prospectus and does not contain all of the information that you need to consider in making your investment decision. You should carefully read the entire prospectus, the applicable prospectus supplement and any related free writing prospectus, including the risks of investing in our shares of common stock discussed under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus. You should also carefully read the information incorporated by reference into this prospectus, including our financial statements, and the exhibits to the registration statement of which this prospectus is a part.

Our Company

We are a clinical-stage biotechnology company focused on discovering and developing innovative protein therapeutics to improve the lives of patients with serious diseases. Each of our product candidates has an innovative mechanism of action and addresses patient populations for which better therapies are needed. Our primary focus is in immuno-oncology, an area in which we have clinical, preclinical, research and discovery programs and collaborations. In addition, we plan to use companion diagnostics where appropriate to allow us to select patients most likely to benefit from treatment with our product candidates. The most advanced product candidates that we or our partners are advancing are identified below.

• Bemarituzumab (FPA144) is an antibody that inhibits fibroblast growth factor receptor 2b, or FGFR2b, that we are studying in a clinical trial in combination with 5-fluorouracil (5-FU), leucovorin and oxaliplatin, a standard-of-care chemotherapy regimen known as mFOLFOX6, as front-line treatment of patients with gastric (stomach) or gastroesophageal junction cancer that overexpresses FGFR2b. In December 2017, we entered into a license and collaboration agreement, or the China collaboration agreement, with Zai Lab (Shanghai) Co., Ltd., or Zai Lab, pursuant to which we granted Zai Lab an exclusive license to develop and commercialize bemarituzumab in China, Hong Kong, Macau and Taiwan.

• Cabiralizumab (FPA008) is an antibody that inhibits colony stimulating factor-1, or CSF1, receptor, or CSF1R, that we and our partner Bristol-Myers Squibb Company, or BMS, are studying in clinical trials in multiple cancers in combination with BMS’s PD-1 immune checkpoint inhibitor, Opdivo^® (nivolumab). In October 2015, we entered into a license and collaboration agreement, or the cabiralizumab collaboration agreement, with BMS pursuant to which we granted BMS an exclusive worldwide license for the development and commercialization of cabiralizumab.

• FPA150 is a CD8 T cell checkpoint inhibitor antibody that targets B7-H4 that we are studying in a clinical trial as monotherapy in multiple cancers.

• FPT155 is a soluble CD80 fusion protein that activates T cells through multiple pathways that we are studying in a clinical trial as monotherapy in multiple cancers.

• BMS-986258 is an anti-T cell immunoglobulin and mucin domain-3, or TIM-3, antibody, that our partner, BMS, is studying in a clinical trial as a single agent and in combination with each of Opdivo and Halozyme Therapeutics, Inc.’s recombinant human hyaluronidase enzyme (rHuPH20) in patients with advanced malignant tumors.

Our differentiated target discovery platform and protein therapeutic capabilities position us to explore pathways in cancer and inflammation and their intersection in immuno-oncology, an area of oncology with significant therapeutic potential and the focus of our activities. We apply our biologics discovery platform to identify and validate targets that we believe could be useful in immuno-oncology and generate and preclinically test therapeutic proteins, including antibodies and fusion proteins, directed to or containing the targets we identify and validate. We plan to continue to advance selected therapeutic candidates into clinical development.

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Corporate Information

We were incorporated under the laws of the State of Delaware in December 2001. Our principal executive office is located at 111 Oyster Point Boulevard, South San Francisco, California 94080, and our telephone number is (415) 365-5600. Our website address is www.fiveprime.com. Our website and the information contained on, or that can be accessed through, our website will not be deemed to be incorporated by reference in, and are not considered part of, this prospectus or any prospectus supplement or free writing prospectus. You should not rely on any such information in making your decision whether to purchase our common stock.

The Shares of Common Stock We May Offer

We may offer shares of our common stock up to a total aggregate offering price of $250,000,000 from time to time in one or more offerings under this prospectus, together with any applicable prospectus supplement and any related free writing prospectus, at prices and on terms to be determined by market conditions at the time of the relevant offering. Each time we offer shares of our common stock under this prospectus, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of offering.

The applicable prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change information contained in this prospectus or in documents we have incorporated by reference. However, no prospectus supplement or free writing prospectus will offer a security other than shares of our common stock.

This prospectus may not be used to consummate a sale of our common stock unless it is accompanied by a prospectus supplement.

We may sell shares of our common stock directly to investors or through underwriters, dealers or agents. We, and our underwriters or agents, reserve the right to accept or reject all or part of any proposed purchase of shares of our common stock. If we do offer shares of our common stock through underwriters or agents, we will include in the applicable prospectus supplement:

• the names of those underwriters or agents;

• applicable fees, discounts and commissions to be paid to them;

• details regarding over-allotment options, if any; and

• the estimated net proceeds to us.

We may issue shares of our common stock from time to time. Each holder of common stock is entitled to one vote for each share of common stock that holder owns on all matters submitted to a vote of the stockholders and does not have cumulative voting rights. Subject to preferences that may apply to any outstanding preferred stock, holders of our common stock are entitled to receive ratably any dividends that our board of directors may declare out of funds legally available for that purpose. In the event of our liquidation, dissolution or winding up, holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preference of any outstanding preferred stock. Holders of our common stock have no preemptive, conversion, subscription or other rights, and there are no redemption or sinking fund provisions applicable to our common stock. We urge you, however, to read the applicable prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) related to any common stock being offered.

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RISK FACTORS

Investing in shares of our common stock involves a high degree of risk. You should carefully review the risks and uncertainties described under the heading “Risk Factors” contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in our Annual Report on Form 10-K for the year ended December 31, 2017 and in our most recent Quarterly Report on Form 10-Q, as updated by our subsequent filings, which are incorporated by reference into this prospectus, before deciding whether to purchase any shares of our common stock being registered pursuant to the registration statement of which this prospectus is a part. Each of these risk factors could adversely affect our business, results of operations, financial condition and cash flows, as well as adversely affect the value of an investment in shares of our common stock, and the occurrence of any of these risks might cause you to lose all or part of your investment. Additional risks not presently known to us or that we currently believe are immaterial may also significantly impair our business operations.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated by reference contain forward-looking statements. These are based on our management’s current beliefs, expectations and assumptions about future events, conditions and results and on information currently available to us. Discussions containing these forward-looking statements may be found, among other places, in the sections titled “Business,” “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” incorporated by reference from our Annual Report on Form 10-K for the year ended December 31, 2017 and in our most recent Quarterly Report on Form 10-Q, as well as any amendments thereto, filed with the SEC.

Any statements in this prospectus, or incorporated herein, about our expectations, beliefs, plans, objectives, assumptions or future events or performance are not historical facts and are forward-looking statements. Within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act, these forward-looking statements include statements regarding:

• our estimates regarding our expenses, revenues, anticipated capital requirements and our needs for additional financing;

• our receipt of future milestone payments or royalties, and the timing of such payments;

• our and our partners’ ability to timely advance drug candidates into and through clinical data readouts and successful completion of clinical trials;

• the timing, progress and results of preclinical studies and research and development programs;

• our expectations regarding the potential safety, efficacy or clinical utility of our product candidates;

• the implementation, timing and likelihood of success of our plans to develop companion diagnostics for our product candidates;

• our ability to establish and maintain collaborations and necessary licenses;

• the implementation of our business model and strategic plans for our business, product candidates and technology;

• the size of patient populations targeted by products we or our partners develop and market adoption of such products by physicians and patients;

• the timing or likelihood of regulatory filings and approvals for products we or our partners develop;

• the ability to negotiate adequate reimbursement and pricing for our drug candidates by third parties and government authorities;

• developments relating to our competitors and our industry; and

• our expectations regarding licensing, acquisitions and strategic operations.

In some cases, you can identify forward-looking statements by terminology such as “anticipate,” “believe,” “could,” “estimate,” “expects,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “will,” “would,” or the negative or plural of any of these terms, and similar expressions intended to identify statements about the future, although not all forward-looking statements contain these words. These statements involve known and unknown risks, uncertainties and other factors that may cause our actual results, levels of activity, performance or achievements to be materially different from the information expressed or implied by these forward-looking statements.

You should refer to the “Risk Factors” section contained in the applicable prospectus supplement and any related free writing prospectus, and under similar headings in the other documents that are incorporated by reference into this prospectus, for a discussion of important factors that may cause our actual results to differ

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materially from those expressed or implied by our forward-looking statements. Given these risks, uncertainties and other factors, many of which are beyond our control, we cannot assure you that the forward-looking statements in this prospectus will prove to be accurate, and you should not place undue reliance on these forward-looking statements. Furthermore, if our forward-looking statements prove to be inaccurate, the inaccuracy may be material. In light of the significant uncertainties in these forward-looking statements, you should not regard these statements as a representation or warranty by us or any other person that we will achieve our objectives and plans in any specified time frame, or at all.

Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to revise any forward-looking statements to reflect events or developments occurring after the date of this prospectus, even if new information becomes available in the future.

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USE OF PROCEEDS

Except as described in any applicable prospectus supplement or in any free writing prospectuses that we may authorize to be provided to you in connection with a specific offering, we currently intend to use the net proceeds from the sale of our shares of common stock offered hereby, if any, for general corporate purposes and working capital requirements. As a result, unless otherwise indicated in any applicable prospectus supplement, our management will have broad discretion to allocate the net proceeds of the offerings. Pending the use of the net proceeds, we intend to invest the net proceeds in a variety of securities, including commercial paper, government and non-government debt securities and/or money market funds that invest in such securities.

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DESCRIPTION OF CAPITAL STOCK

The following description of our capital stock and provisions of our amended and restated certificate of incorporation and amended and restated bylaws are summaries. You should also refer to our amended and restated certificate of incorporation and our amended and restated bylaws, which we have filed with the SEC. See the sections of this prospectus titled “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

General

Under our amended and restated certificate of incorporation, we are authorized to issue up to 100,000,000 shares of common stock, par value $0.001 per share, and 10,000,000 shares of preferred stock, par value $0.001 per share, all of which shares of preferred stock are undesignated. Our board of directors may establish the rights and preferences of the preferred stock from time to time.

Common Stock

Voting Rights

Each holder of common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders. The affirmative vote of holders of at least 66 2/3% of the voting power of all of the then-outstanding shares of capital stock, voting as a single class, will be required to amend certain provisions of our amended and restated certificate of incorporation, including provisions relating to amending our amended and restated bylaws, the classified board, the size of our board, removal of directors, director liability, vacancies on our board, special meetings, stockholder notices, actions by written consent and exclusive jurisdiction.

Dividends

Subject to preferences that may apply to any outstanding preferred stock, holders of our common stock are entitled to receive ratably any dividends that our board of directors may declare out of funds legally available for that purpose on a non-cumulative basis.

Liquidation

In the event of our liquidation, dissolution or winding up, holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preference of any outstanding preferred stock.

Rights and Preferences

Holders of our common stock have no preemptive, conversion, subscription or other rights, and there are no redemption or sinking fund provisions applicable to our common stock. The rights, preferences and privileges of the holders of our common stock are subject to and may be adversely affected by the rights of the holders of shares of any series of our preferred stock that we may designate in the future.

Preferred Stock

Pursuant to our amended and restated certificate of incorporation, our board of directors has the authority, without further action by our stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series and to fix the number, rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences and sinking fund terms, and the number of shares constituting any series or the designation of such

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series, any or all of which may be greater than the rights of holders of our common stock. The issuance of our preferred stock could adversely affect the voting power of holders of common stock and the likelihood that such holders would receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change of control or other corporate action, or make the removal of management more difficult. Additionally, the issuance of preferred stock may have the effect of decreasing the market price of our common stock.

Anti-Takeover Provisions

Section 203 of the General Corporation Law of the State of Delaware

We are subject to Section 203 of the General Corporation Law of the State of Delaware, or the DGCL, which prohibits a Delaware corporation from engaging in any business combination with any interested stockholder for a period of three years after the date that such stockholder became an interested stockholder, unless any of the following exceptions apply:

• before such date, the board of directors of the corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder;

• upon completion of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction began, excluding for purposes of determining the voting stock outstanding, but not the outstanding voting stock owned by the interested stockholder, those shares owned (i) by persons who are directors and also officers of the applicable corporation and (ii) employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or

• on or after such date, the business combination is approved by the board of directors and authorized at an annual or special meeting of the stockholders, and not by written consent, by the affirmative vote of at least 66 2/3% of the outstanding voting stock that is not owned by the interested stockholder.

In general, Section 203 defines a “business combination” to include the following:

• any merger or consolidation involving the corporation and the interested stockholder;

• any sale, transfer, pledge or other disposition of 10% or more of the assets of the corporation involving the interested stockholder;

• subject to certain exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder;

• any transaction involving the corporation that has the effect of increasing the proportionate share of the stock or any class or series of the corporation beneficially owned by the interested stockholder; or

• the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits by or through the corporation.

In general, Section 203 defines an “interested stockholder” as an entity or person who, together with the entity or person’s affiliates and associates, beneficially owns, or is an affiliate or associate of the corporation and within three years prior to the time of determination of interested stockholder status did own, 15% or more of the outstanding voting stock of the corporation.

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Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws

Among other things, our amended and restated certificate of incorporation and amended and restated bylaws will:

• permit our board of directors to issue up to 10,000,000 shares of preferred stock, with any rights, preferences and privileges as they may designate, including the right to approve an acquisition or other change in control;

• provide that the authorized number of directors may be changed only by resolution of our board of directors;

• provide that our board of directors will be classified into three classes of directors;

• provide that, subject to the rights of any series of preferred stock to elect directors, directors may only be removed for cause, which removal may be effected, subject to any limitation imposed by law, by the holders of at least a majority of the voting power of all of our then-outstanding shares of the capital stock entitled to vote generally at an election of directors;

• provide that all vacancies, including newly created directorships, may, except as otherwise required by law, be filled by the affirmative vote of a majority of directors then in office, even if less than a quorum;

• require that any action to be taken by our stockholders must be effected at a duly called annual or special meeting of stockholders and may not be taken by written consent or electronic transmission;

• provide that stockholders seeking to present proposals before a meeting of stockholders or to nominate candidates for election as directors at a meeting of stockholders must provide advance notice in writing, and also specify requirements as to the form and content of a stockholder’s notice;

• provide that special meetings of our stockholders may be called only by the chairman of our board of directors, our chief executive officer or president or by our board of directors pursuant to a resolution adopted by a majority of the total number of authorized directors; and

• not provide for cumulative voting rights, therefore allowing the holders of a majority of the shares of common stock entitled to vote in any election of directors to elect all of the directors standing for election, if they should so choose.

The amendment of any of these provisions would require approval by the holders of at least 66 ²/₃% of the voting power of all our then-outstanding common stock entitled to vote generally in the election of directors, voting together as a single class.

The combination of these provisions will make it more difficult for our stockholders to replace our board of directors as well as for a third party to obtain control of us by replacing our board of directors. Because our board of directors has the power to retain and discharge our officers, these provisions could also make it more difficult for our stockholders or a third party to effect a change in management. In addition, the authorization of undesignated preferred stock makes it possible for our board of directors to issue preferred stock with voting or other rights or preferences that could impede the success of any attempt to change our control.

These provisions are intended to enhance the likelihood of continued stability in the composition of our board of directors and its policies and to discourage coercive takeover practices and inadequate takeover bids. These provisions are also designed to reduce our vulnerability to hostile takeovers and to discourage certain tactics that may be used in proxy fights. However, such provisions could have the effect of discouraging others from making tender offers for our shares and may have the effect of delaying changes in our control or management. As a consequence, these provisions may also inhibit fluctuations in the market price of our stock that could result from actual or rumored takeover attempts. We believe that the benefits of these provisions, including increased protection of our potential ability to negotiate with the proponent of an unfriendly or

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unsolicited proposal to acquire or restructure our company, outweigh the disadvantages of discouraging takeover proposals, because negotiation of takeover proposals could result in an improvement of their terms.

Choice of Forum

Our amended and restated certificate of incorporation provides that unless we consent in writing to the selection of an alternative forum, the Court of Chancery of the State of Delaware will be the exclusive forum for (1) any derivative action or proceeding brought on our behalf, (2) any action asserting a breach of fiduciary duty owed by, or other wrongdoing by, any director, officer, employee or agent to us or our stockholders, (3) any action asserting a claim against us arising pursuant to the DGCL or our certificate of incorporation or bylaws, (4) any action to interpret, apply, enforce or determine the validity of our certificate of incorporation or bylaws, or (5) any action asserting a claim against us that is governed by the internal affairs doctrine.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A. The transfer agent’s address is P.O. Box 505000, Louisville, KY 40233-5000.

Listing

Our common stock is listed on Nasdaq under the symbol “FPRX.”

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PLAN OF DISTRIBUTION

We may sell the shares of our common stock from time to time pursuant to underwritten public offerings, direct sales to the public, negotiated transactions, block trades or a combination of these methods. We may sell the shares of our common stock to or through underwriters or dealers, through agents, or directly to one or more purchasers. We may distribute the shares from time to time in one or more transactions:

• at a fixed price or prices, which may be changed;

• at market prices prevailing at the time of sale;

• at prices related to such prevailing market prices; or

• at negotiated prices.

We may also sell shares of common stock covered by this registration statement in an “at-the-market offering,” as defined in Rule 415 of the Securities Act. Such offering may be made into an existing trading market for such securities in transactions at other than a fixed price, either:

• on or through the facilities of Nasdaq or any other securities exchange or quotation or trading service on which such securities may be listed, quoted or traded at the time of sale; and/or

• other than on Nasdaq or such other securities exchanges or quotation or trading services.

Such at-the-market offerings, if any, may be conducted by underwriters acting as principal or agent.

A prospectus supplement or supplements (and any related free writing prospectus that we may authorize to be provided to you) will describe the terms of the offering of the shares of our common stock, including, to the extent applicable:

• the name or names of any underwriters, dealers or agents, if any;

• the purchase price of the shares of our common stock and the proceeds we will receive from the sale;

• any over-allotment options under which underwriters may purchase additional shares of our common stock from us;

• any agency fees or underwriting discounts and other items constituting agents’ or underwriters’ compensation;

• any public offering price;

• any discounts or concessions allowed or reallowed or paid to dealers; and

• any securities exchange or market on which the shares of our common stock may be listed.

Only underwriters named in the applicable prospectus supplement are underwriters of the shares of our common stock offered by such prospectus supplement.

If underwriters are used in the sale, they will acquire the shares of our common stock for their own account and may resell the shares of our common stock from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligations of the underwriters to purchase the shares of our common stock will be subject to the conditions set forth in the applicable underwriting agreement. We may offer the shares of our common stock to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. Subject to certain conditions, the underwriters will be obligated to purchase all the shares of our common stock offered by the prospectus supplement. Any public offering price and any discounts or concessions allowed or reallowed or paid to dealers may change from time to time. We may use underwriters with whom we have a material relationship. We will identify any such underwriter in the prospectus supplement and describe the nature of such relationship.

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We may sell shares of our common stock directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of shares of our common stock and describe any commissions we will pay the agent in the prospectus supplement. Unless the prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.

We may authorize agents or underwriters to solicit offers by certain types of institutional investors to purchase shares of our common stock from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future. We will describe the conditions to these contracts and the commissions we must pay for solicitation of these contracts in the prospectus supplement.

We may provide agents and underwriters with indemnification against civil liabilities related to this offering, including liabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may make with respect to these liabilities. Agents and underwriters may engage in transactions with, or perform services for, us in the ordinary course of business.

Any underwriter may engage in over-allotment, stabilizing transactions, short-covering transactions and penalty bids. Over-allotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short-covering transactions involve purchases of the shares of our common stock in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the shares of our common stock originally sold by the dealer are purchased in a stabilizing or covering transaction to cover short positions. Those activities may cause the price of the shares of our common stock to be higher than it would otherwise be. If commenced, the underwriters may discontinue any of the activities at any time. These transactions may be effected on any exchange or over-the-counter market or otherwise.

Any underwriters who are qualified market makers on Nasdaq may engage in passive market making transactions in the securities on Nasdaq in accordance with Rule 103 of Regulation M during the business day prior to the pricing of the offering or before the commencement of offers or sales of the common stock. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded. Passive market making may stabilize the market price of the shares of our common stock at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.

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LEGAL MATTERS

Cooley LLP, Palo Alto, California, will pass upon the validity of the shares of common stock offered hereby. Additional legal matters may be passed upon for us or any underwriters, dealers or agents, by counsel that we name in the applicable prospectus supplement.

EXPERTS

Ernst & Young LLP, independent registered public accounting firm, has audited our financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2017, as set forth in their report, which is incorporated by reference in this prospectus and elsewhere in the registration statement. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP’s report, given on their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus is part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and does not contain all the information set forth in the registration statement. Whenever a reference is made in this prospectus to any of our contracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference into this prospectus for a copy of such contract, agreement or other document. We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC’s website at www.sec.gov. We maintain a website at www.fiveprime.com. Information contained in or accessible through our website does not constitute a part of this prospectus.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” information into this prospectus, which means that we can disclose important information to you by referring you to another document filed separately with the SEC. The SEC file number for the documents incorporated by reference in this prospectus is 001-36070. The documents incorporated by reference into this prospectus contain important information that you should read about us.

The following documents are incorporated by reference into this document:

• our Annual Report on Form 10-K for the year ended December 31, 2017, filed with the SEC on February  27, 2018, and as amended on March 12, 2018;

• the information specifically incorporated by reference into our Annual Report on Form 10-K for the year ended December 31, 2017 from our Definitive Proxy Statement on Schedule 14A, filed with the SEC on March 30, 2018;

• our Quarterly Reports on Form 10-Q for the fiscal quarters ended March 31, 2018, June 30, 2018 and September 30, 2018, filed with the SEC on May  8, 2018, August 8, 2018 and November  6, 2018, respectively;

• our Current Reports on Form 8-K filed with the SEC on January 23, 2018, January 25, 2018 (two reports), March  13, 2018, April 9, 2018, April  10, 2018, April 17, 2018, May  11, 2018, June 4, 2018 and November 5, 2018, to the extent the information in such reports is filed and not furnished; and

• the description of our common stock contained in our Registration Statement on Form 8-A, filed with the SEC on September 16, 2013, including any amendments or reports filed for the purposes of updating this description.

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We also incorporate by reference into this prospectus all documents (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (i) after the date of the initial filing of the registration statement of which this prospectus forms a part and prior to effectiveness of the registration statement, or (ii) after the date of this prospectus but prior to the termination of the offering. These documents include periodic reports, such as Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, as well as proxy statements.

We will provide to each person, including any beneficial owner, to whom a prospectus is delivered, without charge upon written or oral request, a copy of any or all of the documents that are incorporated by reference into this prospectus but not delivered with the prospectus, including exhibits that are specifically incorporated by reference into such documents. You should direct any requests for documents to Five Prime Therapeutics, Inc., Attn: Investor Relations, 111 Oyster Point Boulevard, South San Francisco, California 94080; telephone: (415) 365-5737.

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7,200,000 Shares

Common Stock

PROSPECTUS SUPPLEMENT

Cowen		SVB Leerink
	Wedbush PacGrow

November 12, 2020