Curis (CRIS) 424B5 Prospectus supplement for primary offering

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-224627

Up to $30,000,000

PROSPECTUS SUPPLEMENT

(To Prospectus Dated May 17, 2018)

Common Stock

We have entered into a Capital on Demand^™ Sales Agreement with JonesTrading Institutional Services LLC, or JonesTrading, relating to shares of our common stock, $0.01 par value per share, offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the sales agreement, we may offer and sell from time to time shares of our common stock having an aggregate offering price of up to $30,000,000 through JonesTrading, acting as our agent.

Our common stock trades on the Nasdaq Global Market, or Nasdaq, under the symbol “CRIS.” On March 5, 2020, the last reported sale price for our common stock on Nasdaq was $1.28 per share.

Upon our delivery of a placement notice and subject to the terms and conditions of the sales agreement, JonesTrading may sell the common stock by methods deemed to be an “at the market offering” as defined in Rule 415 promulgated under the Securities Act of 1933, as amended, or the Securities Act. JonesTrading will act as sales agent using its commercially reasonable efforts consistent with its normal trading and sales practices and applicable state and federal laws, rules and regulations and the rules of the Nasdaq Stock Market, LLC. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

We will pay JonesTrading a commission for its services in acting as agent and/or principal in the sale of common stock, equal to 3% of the gross sales price per share of all shares sold through it as agent under the sales agreement. In connection with the sales of the common stock on our behalf, JonesTrading will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation paid to JonesTrading will be deemed to be underwriting commissions or discounts. We have agreed in the sales agreement to provide indemnification and contribution to JonesTrading against certain liabilities, including liabilities under the Securities Act.

Investing in our common stock involves a high degree of risk. See “Risk Factors” beginning on Page S-10 of this prospectus supplement, as well as the section captioned “Item 1A—Risk Factors” in our most recently filed annual report onForm 10-K or quarterly report onForm 10-Q which is incorporated by reference into this prospectus supplement, for certain risks you should consider. You should read all of the information set forth in this prospectus supplement and the accompanying prospectus, as well as the documents incorporated by reference herein, carefully before you make your investment decision.

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

March 6, 2020

TABLE OF CONTENTS

Prospectus Supplement

ABOUT THIS PROSPECTUS SUPPLEMENT	S-1
WHERE YOU CAN FIND MORE INFORMATION	S-2
INCORPORATION BY REFERENCE	S-2
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS	S-4
SUMMARY	S-6
THE OFFERING	S-8
RISK FACTORS	S-10
DESCRIPTION OF COMMON STOCK	S-12
USE OF PROCEEDS	S-13
DILUTION	S-14
PLAN OF DISTRIBUTION	S-16
MATERIAL FEDERAL U.S. TAX CONSIDERATIONS FORNON-U.S. HOLDERS OF COMMON STOCK	S-17
LEGAL MATTERS	S-21
EXPERTS	S-21

Prospectus

ABOUT THIS PROSPECTUS	1
WHERE YOU CAN FIND MORE INFORMATION	2
INCORPORATION BY REFERENCE	3
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS	4
CURIS, INC.	5
RISK FACTORS	6
CONSOLIDATED RATIO OF EARNINGS TO COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS	7
USE OF PROCEEDS	8
DESCRIPTION OF CAPITAL STOCK	9
DESCRIPTION OF WARRANTS	15
PLAN OF DISTRIBUTION	16
LEGAL MATTERS	19
EXPERTS	19

ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus relate to the offering of our common stock. Before buying any of the common stock that we are offering, we urge you to carefully read this prospectus supplement and the accompanying prospectus, together with the information incorporated by reference as described under the heading “Incorporation of Certain Information by Reference” in this prospectus supplement. These documents contain important information that you should consider when making your investment decision.

This document is in two parts. The first part, this prospectus supplement, describes the specific terms of the common stock we are offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference herein or therein. 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 herein or 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.

We further note that the representations, warranties and covenants made by us in any agreement that is filed as an exhibit to any document that is incorporated by reference herein or in the accompanying prospectus were made solely for the benefit of the parties to such agreement, including, in some cases, for the purpose of allocating risk among the parties to such agreement, and should not be deemed to be a representation, warranty or covenant to you. Moreover, such representations, warranties or covenants were accurate only as of the date when made. Accordingly, such representations, warranties and covenants should not be relied on as accurately representing the current state of our affairs.

You should rely only on the information contained in or incorporated by reference in this prospectus supplement, the accompanying prospectus and in any free writing prospectus we may authorize for use in connection with this offering. We have not, and JonesTrading has not, authorized anyone to provide any information other than that contained or incorporated by reference in this prospectus supplement, the accompanying prospectus or in any free writing prospectus prepared by or on behalf of us or to which we have referred you. We and JonesTrading take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We are not, and JonesTrading is not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein, and in any free writing prospectus prepared by or on behalf of us that we have authorized for use in connection with this offering is accurate only as of the date of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those dates. You should read this prospectus supplement, the accompanying prospectus, the documents incorporated by reference herein and therein, and any free writing prospectus prepared by or on behalf of us that we may authorize for use in connection with this offering, in their entirety, before making an investment decision. You should also read and consider the information in the documents we have referred you to in the sections of this prospectus supplement and the accompanying prospectus entitled “Where You Can Find More Information” and “Incorporation by Reference.”

Other than in the United States, no action has been taken by us or JonesTrading 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 and the accompanying prospectus may not be offered or sold, directly or indirectly, nor may this prospectus supplement, the accompanying prospectus 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

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applicable rules and regulations of that jurisdiction. Persons into whose possession this prospectus supplement and the accompanying prospectus comes are advised to inform themselves about and to observe any restrictions relating to the offering and the distribution of this prospectus supplement and the accompanying prospectus. This prospectus supplement and the accompanying prospectus does not constitute an offer to sell or a solicitation of an offer to buy any securities offered by this prospectus supplement and the accompanying prospectus in any jurisdiction in which such an offer or a solicitation is unlawful.

Unless the context requires otherwise, all references in this prospectus supplement to “we,” “us,” “our,” “Curis,” the “Company” and similar designations refer to Curis, Inc. and its consolidated subsidiaries. The Curis logo is a trademark of Curis in the United States and in other select countries. We may indicate U.S. trademark registrations and U.S. trademarks with the symbols “^®” and “^™”, respectively. Other third-party logos and product/trade names are registered trademarks or trade names of their respective owners.

WHERE YOU CAN FIND MORE INFORMATION

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 http://www.sec.gov. Copies of certain information filed by us with the SEC are also available on our website at http://www.curis.com. Our website is not a part of this prospectus supplement or the accompanying prospectus and is not incorporated by reference in this prospectus supplement or the accompanying prospectus.

This prospectus supplement and the accompanying prospectus are part of a registration statement we filed with the SEC. This prospectus supplement and the accompanying prospectus omit some information contained in the registration statement in accordance with SEC rules and regulations. You should review the information and exhibits in the registration statement for further information on us and our consolidated subsidiaries and the securities we are offering. Statements in this prospectus supplement and the accompanying prospectus concerning any document we filed as an exhibit to the registration statement or that we otherwise filed with the SEC are not intended to be comprehensive and are qualified by reference to these filings. You should review the complete document to evaluate these statements. You can obtain a copy of the registration statement from the SEC’s website.

INCORPORATION BY REFERENCE

The SEC allows us to incorporate into this prospectus supplement and the accompanying prospectus information that we file with the SEC in other documents. This means that we can disclose important information to you by referring to other documents that contain that information. Any information that we incorporate by reference is considered part of this prospectus supplement and the accompanying prospectus, except in each case for information contained in any filing where we indicate that such information is being furnished or is not to be considered “filed” under the Securities Exchange Act, as amended, or the Exchange Act. Statements contained in documents that we file with the SEC and that are incorporated by reference in this prospectus supplement and the accompanying prospectus will automatically update and supersede information contained in this prospectus supplement and the accompanying prospectus, including information in previously filed documents or reports that have been incorporated by reference in this prospectus supplement and the accompanying prospectus, to the extent the new information differs from or is inconsistent with the old information. This means that you must look at all of the SEC filings that we incorporate by reference to determine if any of the statements in this prospectus supplement, the accompanying prospectus or in any document previously incorporated by reference have been modified or superseded.

We incorporate by reference the documents and other information listed or referred to below(File No. 000-30347) and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (in each

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case, other than those documents or the portions of those documents not deemed to be filed) until all of the securities which this prospectus supplement relates have been sold or the offering is otherwise terminated:

• Annual Report onForm10-K for the fiscal year ended December 31, 2018, filed on March 26, 2019;

• Quarterly Reports on Form10-Q for the quarter ended March 31, 2019, filed onMay 14, 2019, the quarter ended June  30, 2019, filed onAugust 9, 2019, and the quarter ended September  30, 2019, filed onNovember 5, 2019;

• The information specifically incorporated by reference into our Annual Report on Form10-K for the fiscal year ended December 31, 2018 from our Definitive Proxy Statement onSchedule 14A, filed on April 11, 2019;

• Current Reports on Form8-K filedJanuary 3, 2019,May 30, 2019,September  12, 2019,December 6, 2019,December  6, 2019,January 7, 2020,February 6, 2020 andFebruary 27, 2020; and

• The description of our common stock contained in our Registration Statement onForm8-A filed on April 13, 2000, including any amendments or reports filed for the purpose of updating such description. You may request a copy of these filings, at no cost, by writing or telephoning us at the following address or phone number:

Curis, Inc.

4 Maguire Road

Lexington, MA 02421

Attn: Corporate Controller

(617)503-6500

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement, the accompanying prospectus and the documents we incorporate by reference herein and therein include forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, which we refer to as the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, which we refer to as the Exchange Act. For purposes of these statutes, any statement contained in this prospectus supplement, the accompanying prospectus or in the documents we incorporate by reference herein and therein other than a statement of historical fact, may be a forward-looking statement, including statements regarding our strategy, future operations, future financial position, future revenue, projected costs, prospects, plans and objectives of management. In some cases, you can identify forward-looking statements by such terms as “anticipate,” “believe,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “project,” “seek,” “should,” “strategy,” “will,” “would” or other words that convey uncertainty of future events or outcomes to identify these forward-looking statements, although not all forward-looking statements contain these identifying words. Forward-looking statements may include, but are not limited to, statements about:

• the initiation, timing, progress and results of future preclinical studies and clinical trials, and our research and development programs;

• our plans to develop and commercialize our drug candidates;

• our collaborator’s plans to further develop and commercialize Erivedge;

• our ability to establish and maintain collaborations or obtain additional funding;

• the timing or likelihood of regulatory filings and approvals;

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

• our commercialization, marketing and manufacturing capabilities and strategy;

• the rate and degree of market acceptance and clinical utility of our products;

• our competitive position;

• our intellectual property position;

• developments and projections relating to our competitors and our industry;

• the potential of fimepinostat,CA-4948,CI-8993,CA-170,CA-327, and other product candidates that we develop,in-license, or acquire in the future;

• our expectations related to the use of proceeds from this offering;

• our estimates of the period in which we anticipate that existing cash, cash equivalents and investments will enable us to fund our current and planned operations;

• our ability to continue as a going concern;

• our estimated cash, cash equivalents and investments as of December 31, 2019;

• our estimates regarding expenses, future revenue, capital requirements and needs for additional financing; and

• our ability to maintain our listing on the Nasdaq Global Market.

Our actual results may differ materially from those indicated by these forward-looking statements as a result of various important factors, including the factors referred to under the heading “Risk Factors” beginning on pageS-10 of this prospectus supplement, in the “Risk Factors” sections of our Annual Report on Form10-K and Quarterly Reports on Form10-Q and in other filings we make with the SEC from time to time. If one or more of these factors materialize, or if any underlying assumptions prove incorrect, our actual results, performance or achievements may vary materially from any future results, performance or achievements expressed or implied by these forward-looking statements.

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You should consider these factors and the other cautionary statements made in this prospectus supplement, the accompanying prospectus and the documents we incorporate by reference herein and therein as being applicable to all related forward-looking statements wherever they appear in this prospectus supplement, the accompanying prospectus, or the documents incorporated by reference. While we may elect to update forward-looking statements wherever they appear in this prospectus supplement, the accompanying prospectus, or the documents incorporated by reference herein and therein, we do not assume, and specifically disclaim, any obligation to do so, whether as a result of new information, future events or otherwise, except as required by law.

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SUMMARY

This summary highlights information contained elsewhere in this prospectus supplement and the accompanying prospectus and in the documents we incorporate by reference herein and therein. This summary does not contain all of the information that you should consider before deciding to invest in our securities. For a more complete understanding of our company and this offering, you should read carefully this entire prospectus supplement and the accompanying prospectus, including the information incorporated by reference into this prospectus supplement and the accompanying prospectus, and any free writing prospectus that we have authorized for use in connection with this offering, including the “Risk Factors” section beginning on pageS-10 of this prospectus supplement and the “Risk Factors” sections of our Annual Report on Form10-K and Quarterly Reports on Form10-Q, our financial statements and the related notes and the other documents incorporated by reference in this prospectus supplement and the accompanying prospectus.

Company Overview

We are a biotechnology company focused on the development of innovative therapeutics for the treatment of cancer, including fimepinostat, which is being investigated in combination with venetoclax in a Phase 1 clinical study in patients with DLBCL. In 2015, we entered into a collaboration with Aurigene in the areas of immuno-oncology and precision oncology. As part of this collaboration, we have exclusive licenses to oral small molecule antagonists of immune checkpoints including, the VISTA/PDL1 antagonistCA-170, and the TIM3/PDL1 antagonistCA-327, as well as the IRAK4 kinase inhibitor,CA-4948.CA-4948 is currently undergoing testing in a Phase 1 trial in patients withnon-Hodgkin lymphoma. In addition, we are engaged in a collaboration with ImmuNext for development ofCI-8993, a monoclonal anti-VISTA antibody. We are also party to a collaboration with Genentech, a member of the Roche Group, under which Genentech and Roche are commercializing Erivedge^® for the treatment of advanced basal cell carcinoma.

Ability to Continue as Going Concern

As disclosed in our Form10-Q for the quarter ended September 30, 2019, incorporated by reference into this prospectus supplement, based on our then-available cash resources, recurring losses and cash outflows from operations since inception, an expectation of continuing operating losses and cash outflows from operations for the foreseeable future and the need to raise additional capital to finance our future operations, we concluded that we did not have sufficient cash on hand to support current operations for twelve months from the date of filing of our Form10-Q for the quarter ended September 30, 2019, and therefore we determined that there was substantial doubt about our ability to continue as a going concern. The proceeds of this offering, if any, are not expected to alleviate such concern prior to the issuance of our audited financial statements for the fiscal year ended December 31, 2019, or at all. Accordingly, in connection with the future issuance of our audited financial statements for the fiscal year ended December 31, 2019, management expects that it will conclude that there is substantial doubt about our ability to continue as a going concern and we expect the report from our independent registered public accounting firm on such annual financial statements will contain an explanatory paragraph about such substantial doubt about our ability to continue as a going concern. For a further discussion, please refer to “Risk Factors—We have identified conditions and events that raise substantial doubt about our ability to continue as a going concern and the proceeds of this offering are not expected to alleviate such concern” and “Use of Proceeds.”

Company Information

We were organized as a Delaware corporation in February 2000. Our principal executive offices are located at 4 Maguire Road, Lexington, Massachusetts 02421, and our telephone number is(617) 503-6500. Our website is located at www.curis.com. The information contained in, or that can be accessed through, our website is not

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incorporated by reference into this prospectus supplement or the accompanying prospectus and should not be considered to be a part of this prospectus supplement or the accompanying prospectus. Our website address is included as an inactive textual reference only.

Implications of Being a Smaller Reporting Company

We are a “smaller reporting company,” meaning that the market value of our stock held bynon-affiliates is less than $700 million and our annual revenue was less than $100 million during our most recently completed fiscal year. We may continue to be a smaller reporting company if either (i) the market value of our stock held bynon-affiliates is less than $250 million or (ii) our annual revenue was less than $100 million during the most recently completed fiscal year and the market value of our stock held bynon-affiliates is less than $700 million. For so long as we remain a smaller reporting company, we are permitted and intend to rely on exemptions from certain disclosure and other requirements that are applicable to other public companies that are not smaller reporting companies.

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THE OFFERING

Common stock offered by us Shares of our common stock having an aggregate offering price of up to $30,000,000.

Common stock to be outstanding after this offering assuming the sale of all shares in this offering Up to 56,640,371 shares, assuming sales of 23,437,500 shares of our common stock in this offering at a price of $1.28 per share, which was the closing price of our common stock on the Nasdaq Global Market on March 5, 2020. The actual number of shares issued will vary depending on the sales price under this offering.

Manner of offering “At the market offering” that may be made from time to time through our sales agent, JonesTrading Institutional Services LLC. See “Plan of Distribution” onpage S-16.

Use of proceeds We intend to use the net proceeds from the sale of any securities offered under this prospectus supplement for general corporate purposes. Although we have not yet identified specific uses for these proceeds, we currently anticipate using the proceeds for some or all of the following: the conducting of further preclinical testing and clinical studies of our product candidates, the funding of other research and development expenses, thein-licensing of individual drug candidates or drug programs, the acquisition of companies or businesses that complement our business, working capital and capital expenditures.

We have not determined the amount of net proceeds to be used specifically for such purposes. As a result, management will retain broad discretion over the allocation of net proceeds, if any. See “Use of Proceeds” on pageS-13 of this prospectus supplement for a more complete description of the intended use of proceeds from this offering.

Risk factors Investing in our common stock involves a high degree of risk. See “Risk Factors” beginning on pageS-10 of this prospectus supplement, the “Risk Factors” sections of our Annual Report on Form10-K and Quarterly Reports on Form10-Q incorporated by reference into this prospectus supplement, and other information included and incorporated by reference in this prospectus supplement for a discussion of factors you should carefully consider before deciding to invest in our securities.

Nasdaq Global Market symbol “CRIS”

The number of shares of our common stock that will be outstanding immediately after this offering as shown above is based on 33,202,871 shares outstanding as of September 30, 2019 and excludes as of such date:

• 6,012,701 shares of our common stock issuable upon the exercise of outstanding stock options at a weighted average exercise price of $3.48 per share; and

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• an aggregate of 6,985,796 shares of common stock reserved for future issuance under our Third Amended and Restated 2010 Stock Incentive Plan, as amended, and our Amended and Restated 2010 Employee Stock Purchase Plan.

In addition, the discussion and table above do not include 646,551 shares of our common stock issued to Aspire Capital Fund, LLC, or Aspire Capital, in consideration for entering into the Common Stock Purchase Agreement entered into on February 26, 2020, or the Aspire Purchase Agreement, 2,693,965 shares of our common stock initially issued to Aspire Capital for a purchase price of $1.1136 per share pursuant to the Aspire Purchase Agreement or $27.0 million of shares of our common stock that may be sold from time to time to Aspire Capital over the30-month term of the Aspire Purchase Agreement.

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RISK FACTORS

An investment in our common stock involves a high degree of risk. Before deciding whether to invest in our common stock, you should consider carefully the risks described below and discussed under the sections captioned “Risk Factors” contained in Part I—Item 1A of our most recent Annual Report on Form10-K and in our Quarterly Reports on Form10-Q, which are incorporated by reference herein in their entirety, together with other information in this prospectus supplement and the accompanying prospectus, and the information and documents incorporated by reference in this prospectus supplement and the accompanying prospectus, and in any free writing prospectus that we have authorized for use in connection with this offering. If any of these risks actually occurs, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our common stock to decline, resulting in a loss of all or part of your investment.

Additional Risks Related to This Offering

We have broad discretion in how we use the net proceeds of this offering, and we may not use these proceeds effectively or in ways with which you agree.

Our management will have broad discretion as to the application of the net proceeds from this offering, including for any of the purposes described in the section of this prospectus supplement entitled “Use of Proceeds.” You will be relying on the judgment of our management regarding the application of any such proceeds. The results and effectiveness of the use of proceeds are uncertain, and we could spend the proceeds in ways that you do not agree with or that do not improve our results of operations or enhance the value of our common stock. Our failure to apply these funds effectively could have a material adverse effect on our business, delay the development of our drug candidates and cause the price of our common stock to decline.

You may experience immediate and substantial dilution.

The offering prices per share in this offering may exceed the net tangible book value (deficit) per share of our common stock. Assuming that an aggregate of 23,437,500 shares of our common stock are sold at a price of $1.28 per share pursuant to this prospectus supplement, which was the last reported sale price of our common stock on The Nasdaq Global Market on March 5, 2020, for aggregate gross proceeds of $30,000,000, after deducting commissions and estimated aggregate offering expenses payable by us, you would experience immediate dilution of $1.39 per share, representing the difference between our as adjusted net tangible book value (deficit) per share as of September 30, 2019 after giving effect to this offering and the assumed offering price. The exercise of outstanding stock options may result in further dilution of your investment. See the section entitled “Dilution” below for a more detailed illustration of the dilution you would incur if you participate in this offering.

You may experience future dilution as a result of future equity offerings.

We will need additional capital to fund our research and development programs and to fulfill our planned operating goals in addition to sales, if any, in this offering. We may seek additional capital through a combination of private and public equity offerings, including sales of our common stock to Aspire Capital pursuant to the Aspire Purchase Agreement, debt financings, strategic partnerships and alliances and licensing arrangements, which may cause your ownership interest to be diluted. In addition, we have a significant number of options to purchase shares of our common stock outstanding. If these securities are exercised, you may incur further dilution. Moreover, to the extent that we issue additional options to purchase, or securities convertible into or exchangeable for, shares of our common stock in the future and those options or other securities are exercised, converted or exchanged, stockholders may experience further dilution.

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Because we do not anticipate paying any cash dividends on our capital stock in the foreseeable future, capital appreciation, if any, will be your sole source of gain.

We have never declared or paid cash dividends on our capital stock. We anticipate that we will retain our earnings, if any, for future growth and therefore do not anticipate paying cash dividends in the future. As a result, only appreciation of the price of our common stock will provide a return to stockholders.

Future sales of a significant number of our shares of common stock in the public markets, or the perception that such sales could occur, could depress the market price of our shares of common stock or cause it to be highly volatile.

Sales of a substantial number of our shares of common stock in the public markets, or the perception that such sales could occur, could depress the market price of our shares of common stock or cause it to be highly volatile and impair our ability to raise capital through the sale of additional equity securities. A substantial number of shares of common stock are being offered by this prospectus supplement, and we cannot predict if and when shares sold is this offering, if any, will be resold in the public markets. We cannot predict the number of these shares that might be resold nor the effect that future sales of our shares of common stock would have on the market price of our shares of common stock.

We have identified conditions and events that raise substantial doubt about our ability to continue as a going concern and the proceeds of this offering are not expected to alleviate such concern.

As of September 30, 2019, we had $28.0 million in existing cash, cash equivalents and investments. As disclosed in our Form10-Q for the quarter ended September 30, 2019, incorporated by reference into this prospectus supplement, based on our then-available cash resources, recurring losses and cash outflows from operations since inception, an expectation of continuing operating losses and cash outflows from operations for the foreseeable future and the need to raise additional capital to finance our future operations, we concluded that we did not have sufficient cash on hand to support current operations for twelve months from the date of filing of our Form10-Q for the quarter ended September 30, 2019, and therefore we determined that there was substantial doubt about our ability to continue as a going concern.

The potential net proceeds from this offering combined with our existing cash, cash equivalents and investments are not expected to be sufficient to fund our operating expenses and capital expenditure requirements for a period of twelve months from the issuance date of our annual financial statements for the fiscal year ended December 31, 2019. Accordingly, in connection with the future issuance of our audited financial statements for the fiscal year ended December 31, 2019, management expects that it will conclude that there is substantial doubt about our ability to continue as a going concern and we expect the report from our independent registered public accounting firm on such annual financial statements will contain an explanatory paragraph about such substantial doubt about our ability to continue as a going concern.

We expect to finance our operations through this offering, sales to Aspire Capital pursuant to the Aspire Purchase Agreement or other potential equity financings, debt financings or other capital sources. However, we may not be successful in securing additional financing on acceptable terms, or at all. If we are unable to obtain sufficient funding, we may be forced to delay, reduce in scope or eliminate some of our research and development programs, including related clinical trials and operating expenses, potentially delaying the time to market for, or preventing the marketing of, any of our product candidates, which could adversely affect our business prospects and our ability to continue operations, and would have a negative impact on our financial condition and our ability to pursue our business strategies. If we are unable to continue as a going concern, we may have to liquidate our assets and may receive less than the value at which those assets are carried on our audited financial statements, and it is likely that investors will lose all or a part of their investment. Future reports from our independent registered public accounting firm may contain statements expressing substantial doubt about our ability to continue as a going concern. If we seek additional financing to fund our business activities in the future and there remains substantial doubt about our ability to continue as a going concern, investors or other financing sources may be unwilling to provide funding to us on commercially reasonable terms, if at all.

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DESCRIPTION OF COMMON STOCK

Common Stock

The following description of the material terms of our common stock is intended as a summary only and therefore is not a complete description of our common stock. This description is based upon, and is qualified by reference to, our restated certificate of incorporation, as amended, or our certificate of incorporation, our amended and restatedby-laws, as amended, or ourby-laws, and applicable provisions of Delaware corporate law. You should read our certificate of incorporation andby-laws, which are filed as exhibits to our Quarterly Report on Form10-Q for the period ended June 30, 2019 and our Annual Report on Form10-K for the fiscal year ended December 31, 2018, respectively, for the provisions that may be important to you.

Authorized Capital Stock.Our authorized capital stock consists of 101,250,000 shares of common stock and 5,000,000 shares of preferred stock.

Annual Meeting.Annual meetings of our stockholders are held on the date designated in accordance with ourby-laws. Written notice must be mailed to each stockholder entitled to vote not less than ten nor more than 60 days before the date of the meeting. The presence in person or by proxy of the holders of record of a majority of our issued and outstanding shares entitled to vote at such meeting constitutes a quorum for the transaction of business at meetings of the stockholders. Special meetings of the stockholders may be called for any purpose or purposes by the chairman of the board of directors, the chief executive officer (or if there is no chief executive officer, the president) or the board of directors. Except as may be otherwise provided by applicable law, our certificate of incorporation or ourby-laws, all elections shall be decided by a plurality, and all other questions shall be decided by a majority, of the votes cast by stockholders entitled to vote thereon at a duly held meeting of stockholders at which a quorum is present.

Voting Rights.For all matters submitted to a vote of stockholders, each holder of common stock is entitled to one vote for each share registered in his or her name on our books. Our common stock does not have cumulative voting rights. As a result, holders of a majority of our outstanding common stock can elect all of the directors who are up for election in a particular year.

Dividends.If our board of directors declares a dividend, holders of common stock will receive payments from our funds that are legally available to pay dividends. However, this dividend right is subject to any preferential dividend rights we may grant to the persons who hold preferred stock, if any is outstanding.

Liquidation and Dissolution.If we are liquidated or dissolve, the holders of our common stock will be entitled to share ratably in all the assets that remain after we pay our liabilities and any amounts we may owe to the persons who hold preferred stock, if any is outstanding.

Other Rights.Holders of the common stock have no right to:

• convert the stock into any other security;

• have the stock redeemed;

• purchase additional stock; or

• maintain their proportionate ownership interest.

Holders of shares of the common stock are not required to make additional capital contributions.

Transfer Agent and Registrar.Computershare Trust Company, N.A. is transfer agent and registrar for the common stock.

Additional information regarding our capital stock, including a description of certain terms of our certificate of incorporation and ourby-laws and applicable provisions of Delaware corporate law, is set forth under the caption “Description of Capital Stock” beginning on page 9 of the accompanying prospectus.

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USE OF PROCEEDS

We intend to use the net proceeds from the sale of any securities offered under this prospectus supplement for general corporate purposes. General corporate purposes may include the conducting of further preclinical testing and clinical studies of our product candidates, the funding of other research and development expenses, thein-licensing of individual drug candidates or drug programs, the acquisition of companies or businesses that complement our business, working capital and capital expenditures.

The amounts and timing of our use of the net proceeds from the sale of securities in this offering will depend on a number of factors, such as the timing and progress of our and our strategic partners’ clinical trials of our product candidates and our development efforts, the timing and progress of any partnering efforts, technological advances and the competitive environment for our product candidates. As of the date of this prospectus supplement, we cannot specify with certainty all of the particular uses for the net proceeds to us from this offering. Accordingly, our management will have broad discretion in the timing and application of these proceeds. Pending application of the net proceeds as described above, we intend to temporarily invest the proceeds in short-term, interest-bearing instruments.

As disclosed in our Form10-Q for the quarter ended September 30, 2019, incorporated by reference into this prospectus supplement, based on our then-available cash resources, recurring losses and cash outflows from operations since inception, an expectation of continuing operating losses and cash outflows from operations for the foreseeable future and the need to raise additional capital to finance our future operations, we concluded that we did not have sufficient cash on hand to support current operations for twelve months from the date of filing of our Form10-Q for the quarter ended September 30, 2019, and therefore we determined that there was substantial doubt about our ability to continue as a going concern. The proceeds of this offering, if any, are not expected to alleviate such concern prior to the issuance of our audited financial statements for the fiscal year ended December 31, 2019, or at all. Accordingly, in connection with the future issuance of our audited financial statements for the fiscal year ended December 31, 2019, management expects that it will conclude that there is substantial doubt about our ability to continue as a going concern and we expect the report from our independent registered public accounting firm on such annual financial statements will contain an explanatory paragraph about such substantial doubt about our ability to continue as a going concern. For a further discussion, please refer to “Risk Factors – We have identified conditions and events that raise substantial doubt about our ability to continue as a going concern and the proceeds of this offering are not expected to alleviate such concern.”

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DILUTION

If you invest in this offering, your ownership interest will be diluted immediately to the extent of the difference between the public offering price per share and the adjusted net tangible book value (deficit) per share of our common stock after this offering. We calculate net tangible book value (deficit) per share by dividing the net tangible book value, which is tangible assets less total liabilities, by the number of outstanding shares of our common stock. Dilution represents the difference between the amount per share paid by purchasers of shares in this offering and the as adjusted net tangible book value (deficit) per share of our common stock immediately after giving effect to this offering.

Our net tangible book value (deficit) on September 30, 2019 was approximately $(35.0) million, or $(1.05) per share.

After giving effect to the sale of shares of our common stock in the aggregate amount of $30,000,000 in this offering at an assumed offering price of $1.28 per share, which was the last reported sale price of our common stock on the Nasdaq Global Market on March 5, 2020, and after deducting estimated offering commissions and expenses payable by us, our net tangible book value (deficit) as of September 30, 2019 would have been approximately $(6.0) million, or $(0.11) per share of common stock. This represents an immediate increase in net tangible book value (deficit) of $0.94 per share to our existing stockholders and an immediate dilution in net tangible book value (deficit) of $1.39 per share to investors participating in this offering. The following table illustrates this dilution per share to investors participating in this offering:

Assumed offering price per share				$	1.28
Net tangible book value (deficit) per share as of September 30, 2019	$	(1.05	)
Increase per share attributable to new investors	$	0.94
As-adjusted net tangible book value (deficit) per share as of September 30, 2019 after giving effect to this offering				$	(0.11	)
Dilution per share to new investors purchasing shares in the offering				$	1.39

The table above assumes, for illustrative purposes, that an aggregate of 23,437,500 shares of our common stock are sold at a price of $1.28 per share, the last reported sale price of our common stock on the Nasdaq Global Market on March 5, 2020, for aggregate gross proceeds of $30,000,000. The shares sold in this offering, if any, will be sold from time to time at various prices. An increase of $0.250 per share in the price at which the shares are sold from the assumed offering price of $1.28 per share shown in the table above, assuming all of our common stock in the aggregate amount of $30,000,000 is sold at that price, would increase our as adjusted net tangible book value (deficit) per share after the offering to $(0.11) per share and would increase the dilution in net tangible book value (deficit) per share to new investors to $1.64 per share, after deducting commissions and estimated aggregate offering expenses payable by us. A decrease of $0.250 per share in the price at which the shares are sold from the assumed offering price of $1.28 per share shown in the table above, assuming all of our common stock in the aggregate amount of $30,000,000 is sold at that price, would increase our as adjusted net tangible book value (deficit) per share after the offering to $(0.10) per share and would decrease the dilution in net tangible book value (deficit) per share to new investors to $1.13 per share, after deducting commissions and estimated aggregate offering expenses payable by us. This information is supplied for illustrative purposes only.

The above discussion and table are based on 33,202,871 shares outstanding as of September 30, 2019 and excludes as of such date:

• 6,012,701 shares of our common stock issuable upon the exercise of outstanding stock options at a weighted average exercise price of $3.48 per share; and

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• an aggregate of 6,985,796 shares of common stock reserved for future issuance under our Third Amended and Restated 2010 Stock Incentive Plan, as amended, and our Amended and Restated 2010 Employee Stock Purchase Plan.

In addition, the discussion and table above do not include 646,551 shares of our common stock issued to Aspire Capital, in consideration for entering into the Aspire Purchase Agreement, 2,693,965 shares of our common stock initially issued to Aspire Capital for a purchase price of $1.1136 per share pursuant to the Aspire Purchase Agreement or $27.0 million of shares of our common stock that may be sold from time to time to Aspire Capital over the30-month term of the Aspire Purchase Agreement.

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PLAN OF DISTRIBUTION

We have entered into a Capital on Demand^™ Sales Agreement with JonesTrading Institutional Services LLC, or JonesTrading, under which we may issue and sell from time to time up to $30,000,000 of our common stock through JonesTrading as our sales agent. Sales of the common stock, if any, will be made at market prices by any method that is deemed to be an “at the market offering” as defined in Rule 415 under the Securities Act.

JonesTrading will offer the common stock subject to the terms and conditions of the sales agreement on a daily basis or as otherwise agreed upon by us and JonesTrading. We will designate the maximum amount of common stock to be sold through JonesTrading on a daily basis or otherwise determine such maximum amount together with JonesTrading. Subject to the terms and conditions of the sales agreement, JonesTrading will use its commercially reasonable efforts to sell on our behalf all of the shares of common stock requested to be sold by us. We may instruct JonesTrading not to sell common stock if the sales cannot be effected at or above the price designated by us in any such instruction. We or JonesTrading may suspend the offering of the common stock being made through JonesTrading under the sales agreement upon proper notice to the other party. We and JonesTrading each have the right, by giving written notice as specified in the sales agreement, to terminate the sales agreement in each party’s sole discretion at any time.

The aggregate compensation payable to JonesTrading as sales agent shall be equal to 3% of the gross sales price of the shares sold through it pursuant to the sales agreement.

The remaining sales proceeds, after deducting any expenses payable by us and any transaction fees imposed by any governmental, regulatory or self-regulatory organization in connection with the sales, will equal our net proceeds for the sale of such common stock.

JonesTrading will provide written confirmation to us following the close of trading on the Nasdaq Global Market, each day in which common stock is sold through it as sales agent under the sales agreement. Each confirmation will include the number of shares of common stock sold through it as sales agent on that day, the gross sales price per share, the net proceeds to us and the compensation payable by us to JonesTrading.

We will report at least quarterly the number of shares of common stock sold through JonesTrading under the sales agreement, the net proceeds to us and the compensation paid by us to JonesTrading in connection with the sales of common stock.

Settlement for sales of common stock will occur, unless the parties agree otherwise, on the second business day that is also a trading day following the date on which any sales were made in return for payment of the net proceeds to us. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

In connection with the sales of the common stock on our behalf, JonesTrading will be deemed to be an “underwriter” within the meaning of the Securities Act, and the compensation paid to JonesTrading will be deemed to be underwriting commissions or discounts. We have agreed in the sales agreement to provide indemnification and contribution to JonesTrading against certain liabilities, including liabilities under the Securities Act. As sales agent, JonesTrading will not engage in any transactions that stabilize our common stock. In addition, we have agreed to reimburse a portion of the expenses of JonesTrading in connection with this offering up to a maximum of $30,000.

We estimate that the total expenses of the offering payable by us, excluding commissions payable to JonesTrading under the sales agreement, will be approximately $100,000.

JonesTrading and its affiliates may in the future provide various investment banking and other financial services for us and our affiliates for which services they may in the future receive customary fees.

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MATERIAL U.S. FEDERAL INCOME AND ESTATE TAX CONSIDERATIONS FORNON-U.S. HOLDERS OF OUR COMMON STOCK

The following is a discussion of material U.S. federal income and estate tax considerations relating to the ownership and disposition of our common stock by anon-U.S. holder. For purposes of this discussion, the term“non-U.S. holder” means a beneficial owner (other than a partnership or other pass-through entity) of our common stock that is not, for U.S. federal income tax purposes:

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

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

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

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

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 and proposed U.S. Treasury Regulations promulgated thereunder, current administrative rulings and judicial decisions, as in effect as of the date of this prospectus supplement and all of which are subject to change or to differing interpretation, possibly with retroactive effect. Any change or differing interpretation could alter the tax consequences tonon-U.S. holders described in this prospectus supplement. In addition, there can be no assurances that the Internal Revenue Service (IRS) will not challenge one or more of the tax consequences described in this prospectus supplement.

This discussion addresses onlynon-U.S. holders that hold shares of our common stock as a capital asset (generally, property held for investment). This discussion does not address all aspects of U.S. federal income and estate taxation that may be relevant to a particularnon-U.S. holder in light of thatnon-U.S. holder’s individual circumstances nor does it address the alternative minimum tax, the Medicare tax on net investment income or any aspects of U.S. state, local, ornon-U.S. taxes. This discussion also does not consider any specific facts or circumstances that may apply to anon-U.S. holder and does not address the special tax rules applicable to particularnon-U.S. holders, such as:

• insurance companies;

• tax-exempt organizations and governmental organizations;

• financial institutions;

• brokers or dealers in securities;

• pension plans;

• controlled foreign corporations;

• passive foreign investment companies;

• corporations that accumulate earnings to avoid U.S. federal income tax;

• persons who have elected to mark securities to market;

• owners that hold our common stock as part of a straddle, hedge, conversion transaction, synthetic security, or other integrated investment; and

• certain U.S. expatriates.

In addition, this discussion does not address the tax treatment of partnerships (or entities or arrangements that are classified as partnerships for U.S. federal income tax purposes) or persons who hold their common stock through

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partnerships or other entities that are pass-through entities for U.S. federal income tax purposes. A partner in a partnership or other pass-through entity that will hold our common stock should consult his, her or its own tax advisor regarding the tax consequences of the purchase, ownership and disposition of our common stock through a partnership or other pass-through entity, as applicable.

Prospective investors should consult their own tax advisors regarding the U.S. federal, state, local andnon-U.S. income and other tax considerations of acquiring, holding and disposing of our common stock.

Dividends

If we pay distributions on our common stock, those distributions 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 atax-free return of thenon-U.S. holder’s investment, up to such holder’s tax basis in the common stock. Any remaining excess will be treated as capital gain, subject to the tax treatment described below under the heading “—Gain on Disposition of Common Stock.”

Subject to the discussions below regarding effectively connected income, backup withholding and Sections 1471 through 1474 of the Code (commonly referred to as FATCA), dividends paid to anon-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 between the United States and such holder’s country of residence. Anon-U.S. holder of our common stock who claims the benefit of an applicable income tax treaty between the United States and such holder’s country of residence generally will be required to provide a properly executed IRS FormW-8BEN orW-8BEN-E (or successor form) and satisfy applicable certification and other requirements. Anon-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 with the IRS.Non-U.S. holders are urged to consult their own tax advisors regarding their entitlement to benefits under an applicable income tax treaty.

Dividends that are treated as effectively connected with a trade or business conducted by anon-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 thenon-U.S. holder within the United States, are generally exempt from the 30% withholding tax if thenon-U.S. holder furnishes a valid IRS FormW-8ECI (or applicable successor form) to us or our paying agent and satisfies applicable certification and disclosure requirements. However, such U.S. effectively connected income is taxed on a net income basis at the same U.S. federal income tax rates applicable to United States persons (as defined in the Code). Any U.S. effectively connected income received by anon-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 between the United States and such holder’s country of residence.

Gain on Disposition of Common Stock

Anon-U.S. holder generally will not be subject to U.S. federal income tax on gain recognized on a disposition of our common stock unless:

• the gain is effectively connected with thenon-U.S. holder’s conduct of a trade or business in the United States, and if an applicable income tax treaty so provides, the gain is attributable to a permanent establishment or fixed base maintained by thenon-U.S. holder in the United States; in these cases, thenon-U.S. holder will be taxed on a net income basis at the same U.S. federal income tax rates applicable to U.S. persons (as defined in the Code), and if thenon-U.S. holder is a foreign corporation, an additional branch profits tax at a 30% rate, or such lower rates as may be specified by an applicable income tax treaty, may also apply;

• thenon-U.S. holder is a nonresident alien present in the United States for 183 days or more in the taxable year of the disposition and certain other requirements are met, in which case thenon-U.S.

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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 U.S. source capital losses of thenon-U.S. holder, if any; or

• we are or have been at any time during the five-year period preceding such disposition (or thenon-U.S. holder’s holding period, if shorter) a “U.S. real property holding corporation” unless our common stock is regularly traded on an established securities market and thenon-U.S. holder held no more than 5% of our outstanding common stock, directly or indirectly, during the shorter of the five year period ending on the date of the disposition or the period that thenon-U.S. holder held our common stock. If we are determined to be a U.S. real property holding corporation and either our common stock is not regularly traded on an established securities market or anon-U.S. holder holds more than 5% of our outstanding common stock, directly or indirectly, during the applicable testing period, then thenon-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 U.S. persons (as defined in the Code). Generally, a corporation is a “U.S. real property holding corporation” if the fair market value of its “U.S. real property interests” equals or exceeds 50% of the sum of the fair market value of its worldwide real property interests plus its other assets used or held for use in a trade or business. Although there can be no assurance, we believe that we are not currently, and we do not anticipate becoming, a “U.S. real property holding corporation” for U.S. federal income tax purposes. No assurance can be provided that our common stock will be regularly traded on an established securities market for purposes of the rule described above.

Information Reporting and Backup Withholding

We must report annually to the IRS and to eachnon-U.S. holder the gross amount of the distributions on our common stock paid to such holder and the tax withheld, if any, with respect to such distributions.Non-U.S. holders may have to comply with specific certification procedures to establish that the holder is not a U.S. person (as defined in the Code) in order to avoid backup withholding at the applicable rate with respect to dividends on our common stock. Generally, anon-U.S. holder will comply with such procedures if it provides a properly executed IRS FormW-8BEN orW-8BEN-E (or other applicable FormW-8) or otherwise meets documentary evidence requirements for establishing that it is anon-U.S. holder, or otherwise establishes an exemption. Dividends paid tonon-U.S. holders subject to withholding of U.S. federal income tax, as described above under the heading “—Dividends,” will generally be exempt from U.S. backup withholding.

Information reporting and backup withholding generally will apply to the proceeds of a disposition of our common stock by anon-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 anon-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 anon-U.S. holder where the transaction is effected outside the United States through anon-U.S. office of a broker. However, for information reporting purposes, dispositions effected through anon-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 own 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 thenon-U.S. holder resides or is incorporated under the provisions of a specific treaty or agreement.

Backup withholding is not an additional tax. Rather, any amounts withheld under the backup withholding rules from a payment to anon-U.S. holder can be refunded or credited against thenon-U.S. holder’s U.S. federal income tax liability, if any, provided that an appropriate claim is timely filed with the IRS.

FATCA

Provisions of the Code commonly referred to as the Foreign Account Tax Compliance Act, or FATCA, generally impose a 30% withholding tax on dividends on, and gross proceeds from the sale or other disposition of, our

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common stock if paid to a foreign entity unless (i) if the foreign entity is a “foreign financial institution,” the foreign entity undertakes certain due diligence, reporting, withholding, and certification obligations, (ii) if the foreign entity is not a “foreign financial institution,” the foreign entity identifies certain of its U.S. investors, or (iii) the foreign entity is otherwise excepted under FATCA.

Withholding under FATCA generally applies to payments of dividends on our common stock. While withholding under FATCA would also apply to payments of gross proceeds from a sale or other disposition of our common stock under proposed U.S. Treasury Regulations, withholding on payments of gross proceeds is not required. Although such regulations are not final, applicable withholding agents may rely on the proposed regulations until final regulations are issued.

If withholding under FATCA is required on any payment related to our common stock, investors not otherwise subject to withholding (or that otherwise would be entitled to a reduced rate of withholding) on such payment may be required to seek a refund or credit from the IRS. An intergovernmental agreement between the United States and an applicable foreign country may modify the requirements described in this section.Non-U.S. holders should consult their own tax advisors regarding the possible implications of FATCA on their investment in our common stock and the entities through which they hold our common stock.

U.S. Federal Estate Tax

Common stock owned or treated as owned by an individual who is anon-U.S. holder (as specially defined for U.S. federal estate tax purposes) at the time of death will be included in the individual’s gross estate for U.S. federal estate tax purposes and, therefore, may be subject to U.S. federal estate tax, unless an applicable estate tax or other treaty provides otherwise.

The preceding discussion of material U.S. federal tax considerations is for prospective investors’ information only. It is not tax advice. Prospective investors should consult their own tax advisors regarding the particular U.S. federal, state, local, andnon-U.S. tax consequences of purchasing, holding, and disposing of our common stock, including the consequences of any proposed changes in applicable laws.

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LEGAL MATTERS

The validity of the issuance of the common stock offered by this prospectus will be passed upon for us by Wilmer Cutler Pickering Hale and Dorr LLP, Boston, Massachusetts. JonesTrading is being represented in connection with this offering by Duane Morris LLP, New York, New York.

EXPERTS

The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control Over Financial Reporting) incorporated in this prospectus by reference to the Annual Report on Form10-K for the year ended December 31, 2018 have been so incorporated in reliance on the report (which contains an emphasis of matter paragraph relating to the Company’s requirement for additional financing to fund planned future operations as described in Note 1 to the financial statements) of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

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$200,000,000

PROSPECTUS

Common Stock

Preferred Stock

Warrants

We may offer and sell securities from time to time in one or more offerings of up to $200,000,000 in aggregate offering price. This prospectus describes the general terms of these securities and the general manner in which these securities will be offered. We will provide the specific terms of these securities in supplements to this prospectus. The prospectus supplements will also describe the specific manner in which these securities will be offered and may also supplement, update or amend information contained in this document. You should read this prospectus and any applicable prospectus supplement before you invest.

We may offer these securities in amounts, at prices and on terms determined at the time of offering. The securities may be sold directly to you, through agents, or through underwriters and dealers. If agents, underwriters or dealers are used to sell the securities, we will name them and describe their compensation in a prospectus supplement.

Our common stock is listed on the Nasdaq Global Market under the symbol “CRIS.”

Investing in these securities involves certain risks. See “Risk Factors” included in any accompanying prospectus supplement and in the documents incorporated by reference in this prospectus for a discussion of the factors you should carefully consider before deciding to purchase these securities.

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. Any representation to the contrary is a criminal offense.

The date of this prospectus is May 17, 2018.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS	1
WHERE YOU CAN FIND MORE INFORMATION	2
INCORPORATION BY REFERENCE	3
CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS	4
CURIS, INC.	5
RISK FACTORS	6
CONSOLIDATED RATIO OF EARNINGS TO COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS	7
USE OF PROCEEDS	8
DESCRIPTION OF CAPITAL STOCK	9
DESCRIPTION OF WARRANTS	15
PLAN OF DISTRIBUTION	16
LEGAL MATTERS	19
EXPERTS	19

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, which we refer to as the SEC, utilizing a “shelf” registration process. Under this shelf registration process, we may from time to time sell any combination of the securities described in this prospectus in one or more offerings for an aggregate initial offering price of up to $200,000,000.

This prospectus provides you with a general description of the securities we may offer. Each time we sell securities, we will provide one or more prospectus supplements that will contain specific information about the terms of the offering. The prospectus supplement may also add, update or change information contained in this prospectus. You should read both this prospectus and any accompanying prospectus supplement together with the additional information described under the heading “Where You Can Find More Information” beginning on page 2 of this prospectus.

You should rely only on the information contained in or incorporated by reference in this prospectus, any accompanying prospectus supplement or in any related free writing prospectus filed by us with the SEC. We have not authorized anyone to provide you with different information. This prospectus and any accompanying prospectus supplement do not constitute an offer to sell or the solicitation of an offer to buy any securities other than the securities described in this prospectus or such accompanying prospectus supplement or an offer to sell or the solicitation of an offer to buy such securities in any circumstances in which such offer or solicitation is unlawful. You should assume that the information appearing in this prospectus, any prospectus supplement, the documents incorporated by reference and any related free writing prospectus is accurate only as of their respective dates. Our business, financial condition, results of operations and prospects may have changed materially since those dates.

Unless the context requires otherwise, all references in this prospectus to “we,” “us,” “our,” “Curis,” the ��Company” and similar designations refer to Curis, Inc. and its consolidated subsidiaries. The Curis logo is a trademark of Curis in the United States and in other select countries. We may indicate U.S. trademark registrations and U.S. trademarks with the symbols “^®” and “™”, respectively. Other third-party logos and product/trade names are registered trademarks or trade names of their respective owners.

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WHERE YOU CAN FIND MORE INFORMATION

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 http://www.sec.gov. Copies of certain information filed by us with the SEC are also available on our website at http://www.curis.com. Our website is not a part of this prospectus and is not incorporated by reference in this prospectus. You may also read and copy any document we file at the SEC’s Public Reference Room, 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at1-800-SEC-0330 for further information on the operation of the Public Reference Room.

This prospectus is part of a registration statement we filed with the SEC. This prospectus omits some information contained in the registration statement in accordance with SEC rules and regulations. You should review the information and exhibits in the registration statement for further information about us and our consolidated subsidiaries and the securities we are offering. Statements in this prospectus concerning any document we filed as an exhibit to the registration statement or that we otherwise filed with the SEC are not intended to be comprehensive and are qualified by reference to these filings. You should review the complete document to evaluate these statements.

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INCORPORATION BY REFERENCE

The SEC allows us to incorporate by reference much of the information we file with the SEC, which means that we can disclose important information to you by referring you to those publicly available documents. The information that we incorporate by reference in this prospectus is considered to be part of this prospectus. Because we are incorporating by reference future filings with the SEC, this prospectus is continually updated and those future filings may modify or supersede some of the information included or incorporated in this prospectus. This means that you must look at all of the SEC filings that we incorporate by reference to determine if any of the statements in this prospectus or in any document previously incorporated by reference have been modified or superseded.

This prospectus incorporates by reference the documents listed below (FileNo. 000-30347) and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act (in each case, other than those documents or the portions of those documents not deemed to be filed) between the date of the initial registration statement and the effectiveness of the registration statement and following the effectiveness of the registration statement until the offering of the securities under the registration statement is terminated or completed:

• Annual Report onForm10-K for the fiscal year ended December 31, 2017, including the information specifically incorporated by reference into the Annual Report on Form10-K from ourdefinitive proxy statement for the 2018 Annual Meeting of Stockholders;

• Quarterly Report onForm10-Q for the fiscal quarter ended March 31, 2018;

• Current Reports on Form8-K filedJanuary 5, 2018 andMarch 22, 2018; and

• The description of our common stock contained in our Registration Statement onForm8-A filed on April 13, 2000, including any amendments or reports filed for the purpose of updating such description.

You may request a copy of these filings, at no cost, by writing or telephoning us at the following address or telephone number:

Curis, Inc.

4 Maguire Road

Lexington, MA 02421

Attn: Chief Financial Officer

(617)503-6500

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the information incorporated by reference in this prospectus include forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. All statements other than statements of historical fact contained in this prospectus, the information incorporated by reference in this prospectus and any accompanying prospectus supplement are statements that could be deemed forward-looking statements, including, among other things, statements regarding our future discovery and development efforts, our collaborations, our future operating results and financial position, our business strategy, and other objectives for our operations. You can identify these forward-looking statements by their use of words such as “anticipate,” “believe,” “estimate,” “expect,” “forecast,” “intend,” “plan,” “project,” “target,” “will” and other words and terms of similar meaning, although not all forward-looking statements contain these identifying words. Because forward-looking statements relate to the future, they are subject to inherent uncertainties, risks and changes in circumstance that are difficult to predict, and that could cause our actual results to differ materially from those indicated by forward-looking statements. These risks and uncertainties include those inherent in pharmaceutical research and development, such as adverse results in our drug discovery, preclinical trials and clinical development activities, our dependence on our existing and future strategic partners, our ability to obtain any necessary financing to conduct our planned activities, decisions made by the U.S. Food and Drug Administration and other regulatory authorities with respect to the development and commercialization of our drug candidates, our ability to obtain, maintain and enforce intellectual property rights for our drug candidates and other risk factors. We therefore caution you against relying on any of these forward-looking statements, which are only predictions and are subject to risks, uncertainties and assumptions that are referenced in the section of any accompanying prospectus supplement entitled “Risk Factors.” You should also carefully review the risk factors and cautionary statements described in the other documents we file from time to time with the SEC, specifically our most recent Annual Report on Form10-K, our Quarterly Reports on Form10-Q and our Current Reports on Form8-K. Except to the extent required by law, we do not undertake any obligation to revise or update any forward-looking statements.

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CURIS, INC.

We are a biotechnology company seeking to develop and commercialize innovative and effective drug candidates for the treatment of human cancers. Our clinical stage drug candidates are:

• CUDC-907, for which our Phase 2 study in patients with relapsed refractory DLBCL, including those with MYC alterations, is ongoing;

• CA-170, for which we are currently conducting a Phase 1 study in patients with advanced solid tumors and lymphomas; and

• CA-4948, for which in January 2018 we initiated a Phase 1 study in patients with advancednon-Hodgkin lymphomas including those with MYD88 alterations.

Our pipeline also includesCA-327, which is a pre-Investigational New Drug stage oncology drug candidate.

We are party to a collaboration with Roche and Genentech, under which Roche and Genentech are commercializing Erivedge, afirst-in-class orally-administered small molecule Hedgehog signaling pathway inhibitor. Erivedge^® (vismodegib) is approved for the treatment of advanced basal cell carcinoma, or BCC.

In addition, on January 18, 2015, we entered into a collaboration agreement with Aurigene Discovery Technologies Limited, or Aurigene, a specialized, discovery-stage biotechnology company and wholly-owned subsidiary of Dr. Reddy’s Laboratories for the discovery, development and commercialization of small molecule compounds in the areas of immune-oncology and precision oncology, which agreement was amended September 7, 2016. As of March 31, 2018, we have licensed four programs under the Aurigene collaboration: IRAK4 Program—a precision oncology program of small molecule inhibitors of IRAK4 for which the development candidate isCA-4948; PD1/VISTA Program—an immuno-oncology program of small molecule antagonists of PD1 and VISTA immune checkpoint pathways for which the development candidate isCA-170; PD1/TIM3 Program—an immuno-oncology program of small molecule antagonists of PD1 and TIM3 immune checkpoint pathways for which the development candidate isCA-327; and in March 2018, we exercised our option to license a fourth program, which is an immuno-oncology program.

Our principal executive offices are located at 4 Maguire Road, Lexington, Massachusetts 02421, and our telephone number is(617) 503-6500. Our website is located at www.curis.com. The information on our website or any other website is not incorporated by reference into this prospectus or any accompanying prospectus supplement. Our website address is included as an inactive textual reference only.

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RISK FACTORS

An investment in our common stock involves a high degree of risk. Before deciding whether to invest in our common stock, you should consider carefully the risks discussed under the sections captioned “Risk Factors” contained in our most recent Annual Report onForm 10-K as well as our subsequent Quarterly Reports onForm 10-Q and other filings we make with the SEC from time to time, which are incorporated by reference herein in their entirety, together with other information in this prospectus, the information and documents incorporated by reference in this prospectus, and in any prospectus supplement or free writing prospectus that we have authorized for use in connection with an offering to which this prospectus relates. If any of these risks actually occurs, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our common stock to decline, resulting in a loss of all or part of your investment.

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CONSOLIDATED RATIO OF EARNINGS TO COMBINED FIXED CHARGES AND PREFERRED STOCK DIVIDENDS

The following table sets forth our consolidated ratio of earnings to combined fixed charges and preferred stock dividends for each of the periods indicated. You should read this table in conjunction with the consolidated financial statements and notes incorporated by reference in this prospectus.

Three Months Ended

Fiscal Year Ended

March 31, 2018

December 31, 2017

December 31, 2016

December 31, 2015

December 31, 2014

December 31, 2013

Consolidated ratios of earnings to combined fixed charges and preferred stock dividends

N/A

N/A

N/A

N/A

N/A

N/A

For purposes of calculating the ratios above, earnings consist of net income from continuing operations plus provision for income taxes and fixed charges. Fixed charges include interest expense and the interest portion of rent expense which is deemed to be representative of the interest factor.

We did not pay any cash dividends on any shares of our capital stock during the periods set forth above.

We did not record earnings for the three months ended March 31, 2018 or any of the fiscal years ending December 31, 2017, 2016, 2015, 2014 and 2013. Accordingly, our earnings were insufficient to cover fixed charges for such periods and we are unable to disclose a ratio of combined fixed charges and preference dividends to earnings for such periods. The dollar amount of the deficiency in earnings available for fixed charges and preference dividends for the three months ended March 31, 2018 was approximately $10.7 million and for the fiscal years ended December 31, 2017, 2016, 2015, 2014 and 2013 was approximately $53.3 million, $60.4 million, $59.0 million, $18.7 million and $12.3 million, respectively.

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USE OF PROCEEDS

We intend to use the net proceeds from the sale of any securities offered under this prospectus for general corporate purposes unless otherwise indicated in the applicable prospectus supplement. General corporate purposes may include the conducting of further preclinical testing and clinical studies of our product candidates, the funding of other research and development expenses, thein-licensing of individual drug candidates or drug programs, the acquisition of companies or businesses that complement our business, the repayment and refinancing of debt, working capital and capital expenditures. We have not determined the amount of net proceeds to be used specifically for such purposes. As a result, management will retain broad discretion over the allocation of net proceeds.

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DESCRIPTION OF CAPITAL STOCK

The following description of our capital stock is intended as a summary only and therefore is not a complete description of our capital stock. This description is based upon, and is qualified by reference to, our restated certificate of incorporation, as amended, or our certificate of incorporation, our amended and restatedby-laws, as amended, or ourby-laws, and applicable provisions of Delaware corporate law. You should read our certificate of incorporation andby-laws, which are filed as exhibits to the registration statement of which this prospectus forms a part, for the provisions that are important to you.

Our authorized capital stock consists of 225,000,000 shares of common stock and 5,000,000 shares of preferred stock. At our 2018 annual meeting of stockholders to be held on May 15, 2018, we are seeking stockholder approval to increase the number of shares of common stock authorized for issuance under our certificate of incorporation to 337,500,000.

Common Stock

Annual Meeting.Annual meetings of our stockholders are held on the date designated in accordance with ourby-laws. Written notice must be mailed to each stockholder entitled to vote not less than ten nor more than 60 days before the date of the meeting. The presence in person or by proxy of the holders of record of a majority of our issued and outstanding shares entitled to vote at such meeting constitutes a quorum for the transaction of business at meetings of the stockholders. Special meetings of the stockholders may be called for any purpose or purposes by the chairman of the board of directors, the chief executive officer (or if there is no chief executive officer, the president) or the board of directors. Except as may be otherwise provided by applicable law, our certificate of incorporation or ourby-laws, all elections shall be decided by a plurality, and all other questions shall be decided by a majority, of the votes cast by stockholders entitled to vote thereon at a duly held meeting of stockholders at which a quorum is present.

Voting Rights. For all matters submitted to a vote of stockholders, each holder of common stock is entitled to one vote for each share registered in his or her name on our books. Our common stock does not have cumulative voting rights. As a result, holders of a majority of our outstanding common stock can elect all of the directors who are up for election in a particular year.

Dividends. If our board of directors declares a dividend, holders of common stock will receive payments from our funds that are legally available to pay dividends. However, this dividend right is subject to any preferential dividend rights we may grant to the persons who hold preferred stock, if any is outstanding.

Liquidation and Dissolution. If we are liquidated or dissolve, the holders of our common stock will be entitled to share ratably in all the assets that remain after we pay our liabilities and any amounts we may owe to the persons who hold preferred stock, if any is outstanding.

Other Rights. Holders of the common stock have no right to:

• convert the stock into any other security;

• have the stock redeemed;

• purchase additional stock; or

• maintain their proportionate ownership interest.

Holders of shares of the common stock are not required to make additional capital contributions.

Transfer Agent and Registrar. Computershare Trust Company, N.A. is transfer agent and registrar for the common stock.

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Preferred Stock

As of March 31, 2018, no shares of preferred stock were outstanding.

We are authorized to issue “blank check” preferred stock, which may be issued in one or more series upon authorization of our board of directors. Our board of directors is authorized to fix the designation of the series, the number of authorized shares of the series, dividend rights and terms, conversion rights, voting rights, redemption rights and terms, liquidation preferences and any other rights, powers, preferences and limitations applicable to each series of preferred stock. The authorized shares of our preferred stock are available for issuance without further action by our stockholders, unless such action is required by applicable law or the rules of any stock exchange on which our securities may be listed. If the approval of our stockholders is not required for the issuance of shares of our preferred stock, our board may determine not to seek stockholder approval. The specific terms of any series of preferred stock offered pursuant to this prospectus will be described in the prospectus supplement relating to that series of preferred stock.

A series of our preferred stock could, depending on the terms of such series, impede the completion of a merger, tender offer or other takeover attempt. Our board of directors will make any determination to issue preferred shares based upon its judgment as to the best interests of our stockholders. Our directors, in so acting, could issue preferred stock having terms that could discourage an acquisition attempt through which an acquirer may be able to change the composition of our board of directors, including a tender offer or other transaction that some, or a majority, of our stockholders might believe to be in their best interests or in which stockholders might receive a premium for their stock over the then-current market price of the stock.

The preferred stock has the terms described below unless otherwise provided in the prospectus supplement relating to a particular series of preferred stock. You should read the prospectus supplement relating to the particular series of preferred stock being offered for specific terms, including:

• the designation and stated value per share of the preferred stock and the number of shares offered;

• the amount of liquidation preference per share;

• the price at which the preferred stock will be issued;

• the dividend rate, or method of calculation of dividends, the dates on which dividends will be payable, whether dividends will be cumulative or noncumulative and, if cumulative, the dates from which dividends will commence to accumulate;

• any redemption or sinking fund provisions;

• if other than the currency of the United States, the currency or currencies including composite currencies in which the preferred stock is denominated and/or in which payments will or may be payable;

• any conversion provisions; and

• any other rights, preferences, privileges, limitations and restrictions on the preferred stock.

The preferred stock will, when issued, be fully paid andnon-assessable. Unless otherwise specified in the prospectus supplement, each series of preferred stock will rank equally as to dividends and liquidation rights in all respects with each other series of preferred stock. The rights of holders of shares of each series of preferred stock will be subordinate to those of our general creditors.

Rank. Unless otherwise specified in the prospectus supplement, the preferred stock will, with respect to dividend rights and rights upon our liquidation, dissolution or winding up of our affairs, rank:

• senior to our common stock and to all equity securities ranking junior to such preferred stock with respect to dividend rights or rights upon our liquidation, dissolution or winding up of our affairs;

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• on a parity with all equity securities issued by us, the terms of which specifically provide that such equity securities rank on a parity with the preferred stock with respect to dividend rights or rights upon our liquidation, dissolution or winding up of our affairs; and

• junior to all equity securities issued by us, the terms of which specifically provide that such equity securities rank senior to the preferred stock with respect to dividend rights or rights upon our liquidation, dissolution or winding up of our affairs.

The term “equity securities” does not include convertible debt securities.

Dividends. Holders of the preferred stock of each series will be entitled to receive, when, as and if declared by our board of directors, cash dividends at such rates and on such dates described in the prospectus supplement. Different series of preferred stock may be entitled to dividends at different rates or based on different methods of calculation. The dividend rate may be fixed or variable or both. Dividends will be payable to the holders of record as they appear on our stock books on record dates fixed by our board of directors, as specified in the applicable prospectus supplement.

Dividends on any series of preferred stock may be cumulative or noncumulative, as described in the applicable prospectus supplement. If our board of directors does not declare a dividend payable on a dividend payment date on any series of noncumulative preferred stock, then the holders of that noncumulative preferred stock will have no right to receive a dividend for that dividend payment date, and we will have no obligation to pay the dividend accrued for that period, whether or not dividends on that series are declared payable on any future dividend payment dates. Dividends on any series of cumulative preferred stock will accrue from the date we initially issue shares of such series or such other date specified in the applicable prospectus supplement.

No dividends may be declared or paid or funds set apart for the payment of any dividends on any parity securities unless full dividends have been paid or set apart for payment on the preferred stock. If full dividends are not paid, the preferred stock will share dividends pro rata with the parity securities.

No dividends may be declared or paid or funds set apart for the payment of dividends on any junior securities unless full dividends for all dividend periods terminating on or prior to the date of the declaration or payment will have been paid or declared and a sum sufficient for the payment set apart for payment on the preferred stock.

Liquidation Preference. Upon any voluntary or involuntary liquidation, dissolution or winding up of our affairs, then, before we make any distribution or payment to the holders of any common stock or any other class or series of our capital stock ranking junior to the preferred stock in the distribution of assets upon any liquidation, dissolution or winding up of our affairs, the holders of each series of preferred stock shall be entitled to receive out of assets legally available for distribution to stockholders, liquidating distributions in the amount of the liquidation preference per share set forth in the prospectus supplement, plus any accrued and unpaid dividends thereon. Such dividends will not include any accumulation in respect of unpaid noncumulative dividends for prior dividend periods. Unless otherwise specified in the prospectus supplement, after payment of the full amount of their liquidating distributions, the holders of preferred stock will have no right or claim to any of our remaining assets. Upon any such voluntary or involuntary liquidation, dissolution or winding up, if our available assets are insufficient to pay the amount of the liquidating distributions on all outstanding preferred stock and the corresponding amounts payable on all other classes or series of our capital stock ranking on parity with the preferred stock and all other such classes or series of shares of capital stock ranking on parity with the preferred stock in the distribution of assets, then the holders of the preferred stock and all other such classes or series of capital stock will share ratably in any such distribution of assets in proportion to the full liquidating distributions to which they would otherwise be entitled.

Upon any such liquidation, dissolution or winding up and if we have made liquidating distributions in full to all holders of preferred stock, we will distribute our remaining assets among the holders of any other classes or

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series of capital stock ranking junior to the preferred stock according to their respective rights and preferences and, in each case, according to their respective number of shares. For such purposes, our consolidation or merger with or into any other corporation, trust or entity, or the sale, lease or conveyance of all or substantially all of our property or assets will not be deemed to constitute a liquidation, dissolution or winding up of our affairs.

Redemption. If so provided in the applicable prospectus supplement, the preferred stock will be subject to mandatory redemption or redemption at our option, as a whole or in part, in each case upon the terms, at the times and at the redemption prices set forth in such prospectus supplement.

The prospectus supplement relating to a series of preferred stock that is subject to mandatory redemption will specify the number of shares of preferred stock that shall be redeemed by us in each year commencing after a date to be specified, at a redemption price per share to be specified, together with an amount equal to all accrued and unpaid dividends thereon to the date of redemption. Unless the shares have a cumulative dividend, such accrued dividends will not include any accumulation in respect of unpaid dividends for prior dividend periods. We may pay the redemption price in cash or other property, as specified in the applicable prospectus supplement. If the redemption price for preferred stock of any series is payable only from the net proceeds of the issuance of shares of our capital stock, the terms of such preferred stock may provide that, if no such shares of our capital stock shall have been issued or to the extent the net proceeds from any issuance are insufficient to pay in full the aggregate redemption price then due, such preferred stock shall automatically and mandatorily be converted into the applicable shares of our capital stock pursuant to conversion provisions specified in the applicable prospectus supplement. Notwithstanding the foregoing, we will not redeem any preferred stock of a series unless:

• if that series of preferred stock has a cumulative dividend, we have declared and paid or contemporaneously declare and pay or set aside funds to pay full cumulative dividends on the preferred stock for all past dividend periods and the then current dividend period; or

• if such series of preferred stock does not have a cumulative dividend, we have declared and paid or contemporaneously declare and pay or set aside funds to pay full dividends for the then current dividend period.

In addition, we will not acquire any preferred stock of a series unless:

• if that series of preferred stock has a cumulative dividend, we have declared and paid or contemporaneously declare and pay or set aside funds to pay full cumulative dividends on all outstanding shares of such series of preferred stock for all past dividend periods and the then current dividend period; or

• if that series of preferred stock does not have a cumulative dividend, we have declared and paid or contemporaneously declare and pay or set aside funds to pay full dividends on the preferred stock of such series for the then current dividend period.

However, at any time we may purchase or acquire preferred stock of that series (1) pursuant to a purchase or exchange offer made on the same terms to holders of all outstanding preferred stock of such series or (2) by conversion into or exchange for shares of our capital stock ranking junior to the preferred stock of such series as to dividends and upon liquidation.

If fewer than all of the outstanding shares of preferred stock of any series are to be redeemed, we will determine the number of shares that may be redeemed pro rata from the holders of record of such shares in proportion to the number of such shares held or for which redemption is requested by such holder or by any other equitable manner that we determine. Such determination will reflect adjustments to avoid redemption of fractional shares.

Unless otherwise specified in the prospectus supplement, we will mail notice of redemption at least 30 days but not more than 60 days before the redemption date to each holder of record of preferred stock to be redeemed at the address shown on our stock transfer books. Each notice shall state:

• the redemption date;

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• the number of shares and series of preferred stock to be redeemed;

• the redemption price;

• the place or places where certificates for such preferred stock are to be surrendered for payment of the redemption price;

• that dividends on the shares to be redeemed will cease to accrue on such redemption date;

• the date on which the holder’s conversion rights, if any, as to such shares shall terminate; and

• the specific number of shares to be redeemed from each such holder if fewer than all the shares of any series are to be redeemed.

If notice of redemption has been given and we have set aside the funds necessary for such redemption in trust for the benefit of the holders of any shares called for redemption, then from and after the redemption date, dividends will cease to accrue on such shares, and all rights of the holders of such shares will terminate, except the right to receive the redemption price.

Voting Rights. Holders of preferred stock will not have any voting rights, except as required by law or as indicated in the applicable prospectus supplement.

Unless otherwise provided for under the terms of any series of preferred stock, no consent or vote of the holders of shares of preferred stock or any series thereof shall be required for any amendment to our certificate of incorporation that would increase the number of authorized shares of preferred stock or the number of authorized shares of any series thereof or decrease the number of authorized shares of preferred stock or the number of authorized shares of any series thereof (but not below the number of authorized shares of preferred stock or such series, as the case may be, then outstanding).

Conversion Rights. The terms and conditions, if any, upon which any series of preferred stock is convertible into our common stock will be set forth in the applicable prospectus supplement relating thereto. Such terms will include the number of shares of common stock into which the shares of preferred stock are convertible, the conversion price, rate or manner of calculation thereof, the conversion period, provisions as to whether conversion will be at our option or at the option of the holders of the preferred stock, the events requiring an adjustment of the conversion price and provisions affecting conversion in the event of the redemption.

Transfer Agent and Registrar. The transfer agent and registrar for the preferred stock will be set forth in the applicable prospectus supplement.

Provisions of Our Certificate of Incorporation andBy-laws and Delaware Law That May Have Anti-Takeover Effects

Board of Directors. Ourby-laws provide for a board of directors divided as nearly equally as possible into three classes. Each class is elected to a term expiring at the annual meeting of stockholders held in the third year following the year of such election. The number of directors comprising our board of directors is fixed from time to time by the board of directors.

Removal of Directors by Stockholders. Ourby-laws provide that directors may be removed only for cause by the affirmative vote of the holders of 75% of the shares of our capital stock issued, outstanding and entitled to vote. Ourby-laws require the affirmative vote of the holders of at least 75% of our outstanding voting securities to amend or repeal the provision relating to the division of our board of directors into three classes.

Stockholder Nomination of Directors. Ourby-laws provide that a stockholder must notify us in writing of any stockholder nomination of a director not earlier than the 90th day and not later than the 60th day prior to such

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meeting; provided, if less than 70 days’ notice or prior public disclosure of the date of the meeting is given to stockholders, such nomination shall have been mailed or delivered to the Secretary not later than the close of business on the 10th day following the date on which the notice of the meeting was mailed or such public disclosure was made, whichever occurs first.

No Action By Written Consent. Our certificate of incorporation provides that our stockholders may not act by written consent and may only act at duly called meetings of stockholders.

Delaware Business Combination Statute. Section 203 of the General Corporation Law of the State of Delaware, which we refer to as the DGCL, is applicable to us. Section 203 of the DGCL restricts some types of transactions and business combinations between a corporation and a 15% stockholder. A 15% stockholder is generally considered by Section 203 to be a person owning 15% or more of the corporation’s outstanding voting stock. Section 203 refers to a 15% stockholder as an “interested stockholder.” Section 203 restricts these transactions for a period of three years from the date the stockholder acquires 15% or more of our outstanding voting stock. With some exceptions, unless the transaction is approved by the board of directors and the holders of at leasttwo-thirds of the outstanding voting stock of the corporation, Section 203 prohibits significant business transactions such as:

• a merger with, disposition of significant assets to or receipt of disproportionate financial benefits by the interested stockholder, and

• any other transaction that would increase the interested stockholder’s proportionate ownership of any class or series of our capital stock.

The shares held by the interested stockholder are not counted as outstanding when calculating thetwo-thirds of the outstanding voting stock needed for approval.

The prohibition against these transactions does not apply if:

• prior to the time that any stockholder became an interested stockholder, the board of directors approved either the business combination or the transaction in which such stockholder acquired 15% or more of our outstanding voting stock, or

• the interested stockholder owns at least 85% of our outstanding voting stock as a result of a transaction in which such stockholder acquired 15% or more of our outstanding voting stock. Shares held by persons who are both directors and officers or by some types of employee stock plans are not counted as outstanding when making this calculation.

Directors’ Liability

Our certificate of incorporation provides that a member of the board of directors will not be personally liable to us or our stockholders for monetary damages for breaches of their legal duties to us or our stockholders as a director, except for liability:

• for any breach of the director’s legal duty to act in the best interests of us and our stockholders;

• for acts or omissions by the director with dishonest intentions or which involve intentional misconduct or an intentional violation of the law;

• for declaring dividends or authorizing the purchase or redemption of shares in violation of Delaware law; or

• for transactions where the director derived an improper personal benefit.

Our certificate of incorporation also allows us to indemnify directors and officers to the fullest extent authorized by Delaware law, and we have entered into indemnification agreements with our directors.

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DESCRIPTION OF WARRANTS

We may issue warrants to purchase preferred stock or common stock. We may offer warrants separately or together with one or more additional warrants, preferred stock or common stock, or any combination of those securities in the form of units, as described in the applicable prospectus supplement. If we issue warrants as part of a unit, the accompanying prospectus supplement will specify whether those warrants may be separated from the other securities in the unit prior to the expiration date of the warrants. The applicable prospectus supplement will also describe the following terms of any warrants:

• the specific designation and aggregate number of, and the offering price at which we will issue, the warrants;

• the currency or currency units in which the offering price, if any, and the exercise price are payable;

• the date on which the right to exercise the warrants will begin and the date on which that right will expire or, if you may not continuously exercise the warrants throughout that period, the specific date or dates on which you may exercise the warrants;

• whether the warrants are to be sold separately or with other securities as parts of units;

• whether the warrants will be issued in definitive or global form or in any combination of these forms, although, in any case, the form of a warrant included in a unit will correspond to the form of the unit and of any security included in that unit;

• any applicable material U.S. federal income tax consequences;

• the identity of the warrant agent for the warrants and of any other depositaries, execution or paying agents, transfer agents, registrars or other agents;

• the proposed listing, if any, of the warrants or any securities purchasable upon exercise of the warrants on any securities exchange;

• the designation and terms of any equity securities purchasable upon exercise of the warrants;

• if applicable, the designation and terms of the preferred stock or common stock with which the warrants are issued and the number of warrants issued with each security;

• if applicable, the date from and after which any warrants issued as part of a unit and the related preferred stock or common stock will be separately transferable;

• the number of shares of preferred stock or the number of shares of common stock purchasable upon exercise of a warrant and the price at which those shares may be purchased;

• if applicable, the minimum or maximum amount of the warrants that may be exercised at any one time;

• information with respect to book-entry procedures, if any;

• the anti-dilution provisions of, and other provisions for changes to or adjustment in the exercise price of, the warrants, if any;

• any redemption or call provisions; and

• any additional terms of the warrants, including terms, procedures and limitations relating to the exchange or exercise of the warrants.

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PLAN OF DISTRIBUTION

We may sell securities:

• through underwriters;

• through dealers;

• through agents;

• directly to purchasers; or

• through a combination of any of these methods of sale.

In addition, we may issue the securities as a dividend or distribution or in a subscription rights offering to our existing security holders. This prospectus may be used in connection with any offering of our securities through any of these methods or other methods described in the applicable prospectus supplement.

We may directly solicit offers to purchase securities, or agents may be designated to solicit such offers. We will, in the prospectus supplement relating to such offering, name any agent that could be viewed as an underwriter under the Securities Act, and describe any commissions that we must pay. Any such agent will be acting on a best efforts basis for the period of its appointment or, if indicated in the applicable prospectus supplement, on a firm commitment basis.

The distribution of the securities may be effected from time to time in one or more transactions:

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

• at market prices prevailing at the time of sale;

• at prices related to such prevailing market prices; or

• at negotiated prices.

Each prospectus supplement will describe the method of distribution of the securities and any applicable restrictions.

The prospectus supplement with respect to the securities of a particular series will describe the terms of the offering of the securities, including the following:

• the name of the agent or any underwriters;

• the public offering or purchase price and the proceeds we will receive from the sale of the securities;

• any discounts and commissions to be allowed orre-allowed or paid to the agent or underwriters;

• all other items constituting underwriting compensation;

• any discounts and commissions to be allowed orre-allowed or paid to dealers; and

• any exchanges on which the securities will be listed.

If any underwriters or agents are utilized in the sale of the securities in respect of which this prospectus is delivered, we will enter into an underwriting agreement or other agreement with them at the time of sale to them, and we will set forth in the prospectus supplement relating to such offering the names of the underwriters or agents and the terms of the related agreement with them.

If a dealer is utilized in the sale of the securities in respect of which this prospectus is delivered, we will sell such securities to the dealer, as principal. The dealer may then resell such securities to the public at varying prices to be determined by such dealer at the time of resale.

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If we offer securities in a subscription rights offering to our existing security holders, we may enter into a standby underwriting agreement with dealers, acting as standby underwriters. We may pay the standby underwriters a commitment fee for the securities they commit to purchase on a standby basis. If we do not enter into a standby underwriting arrangement, we may retain a dealer-manager to manage a subscription rights offering for us.

Remarketing firms, agents, underwriters, dealers and other persons may be entitled under agreements which they may enter into with us to indemnification by us against certain civil liabilities, including liabilities under the Securities Act, and may be customers of, engage in transactions with or perform services for us in the ordinary course of business.

If so indicated in the applicable prospectus supplement, we will authorize underwriters or other persons acting as our agents to solicit offers by certain institutions to purchase securities from us pursuant to delayed delivery contracts providing for payment and delivery on the date stated in the prospectus supplement. Each contract will be for an amount not less than, and the aggregate amount of securities sold pursuant to such contracts shall not be less nor more than, the respective amounts stated in the prospectus supplement. Institutions with whom the contracts, when authorized, may be made include commercial and savings banks, insurance companies, pension funds, investment companies, educational and charitable institutions and other institutions, but shall in all cases be subject to our approval. Delayed delivery contracts will not be subject to any conditions except that:

• the purchase by an institution of the securities covered under that contract shall not at the time of delivery be prohibited under the laws of the jurisdiction to which that institution is subject; and

• if the securities are also being sold to underwriters acting as principals for their own account, the underwriters shall have purchased such securities not sold for delayed delivery. The underwriters and other persons acting as our agents will not have any responsibility in respect of the validity or performance of delayed delivery contracts.

Certain agents, underwriters and dealers, and their associates and affiliates may be customers of, have borrowing relationships with, engage in other transactions with, and/or perform services, including investment banking services, for us or one or more of our respective affiliates in the ordinary course of business.

In order to facilitate the offering of the securities, any underwriters may engage in transactions that stabilize, maintain or otherwise affect the price of the securities or any other securities the prices of which may be used to determine payments on such securities. Specifically, any underwriters may overallot in connection with the offering, creating a short position for their own accounts. In addition, to cover overallotments or to stabilize the price of the securities or of any such other securities, the underwriters may bid for, and purchase, the securities or any such other securities in the open market. Finally, in any offering of the securities through a syndicate of underwriters, the underwriting syndicate may reclaim selling concessions allowed to an underwriter or a dealer for distributing the securities in the offering if the syndicate repurchases previously distributed securities in transactions to cover syndicate short positions, in stabilization transactions or otherwise. Any of these activities may stabilize or maintain the market price of the securities above independent market levels. Any such underwriters are not required to engage in these activities and may end any of these activities at any time.

Under Rule15c6-1 of the Exchange Act, trades in the secondary market generally are required to settle in two business days, unless the parties to any such trade expressly agree otherwise or the securities are sold by us to an underwriter in a firm commitment underwritten offering. The applicable prospectus supplement may provide that the original issue date for your securities may be more than two scheduled business days after the trade date for your securities. Accordingly, in such a case, if you wish to trade securities on any date prior to the second business day before the original issue date for your securities, you will be required, by virtue of the fact that your securities initially are expected to settle in more than two scheduled business days after the trade date for your securities, to make alternative settlement arrangements to prevent a failed settlement.

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The securities may be new issues of securities and may have no established trading market. The securities may or may not be listed on a national securities exchange. We can make no assurance as to the liquidity of or the existence of trading markets for any of the securities.

To the extent applicable, in compliance with the guidelines of the Financial Industry Regulatory Authority, or FINRA, the aggregate maximum discount, commission or agency fees or other items constituting underwriting compensation to be received by any FINRA member or independent broker-dealer will not exceed 8% of the proceeds from any offering pursuant to this prospectus and any applicable prospectus supplement.

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LEGAL MATTERS

Unless the applicable prospectus supplement indicates otherwise, the validity of the securities in respect of which this prospectus is being delivered will be passed upon by Wilmer Cutler Pickering Hale and Dorr LLP.

EXPERTS

The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control Over Financial Reporting) incorporated in this prospectus by reference to the Annual Report on Form10-K for the year ended December 31, 2017 have been so incorporated in reliance on the report (which contains an explanatory paragraph relating to the Company’s liquidity as described in Note 1 to the financial statements) of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

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Up to $30,000,000

Common Stock

PROSPECTUS SUPPLEMENT

March 6, 2020