Merrimack Pharmaceuticals (MACK) 10-Q 2 Nov 23 2023 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Oct. 31, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Trading Symbol	MACK
Entity Registrant Name	MERRIMACK PHARMACEUTICALS INC
Entity Central Index Key	0001274792
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		14,320,953
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common stock, $0.01 par value
Security Exchange Name	NASDAQ
Entity File Number	001-35409
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3210530
Entity Address, Address Line One	One Broadway
Entity Address, Address Line Two	14th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	720-8606
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 6,083,000	$ 19,439,000
Short-term investments	12,821,000	0
Prepaid expenses and other current assets	390,000	389,000
Total current assets	19,294,000	19,828,000
Other assets	5,000	8,000
Total assets	19,299,000	19,836,000
Current liabilities:
Accounts payable, accrued expenses and other	493,000	589,000
Total current liabilities	493,000	589,000
Total liabilities	493,000	589,000
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.01 par value: 10,000 shares authorized at September 30, 2023 and December 31, 2022; no shares issued or outstanding at September 30, 2023 or December 31, 2022
Common stock, $0.01 par value: 30,000 shares authorized at September 30, 2023 and December 31, 2022; 14,321 and 14,215 shares issued and outstanding at September 30, 2023 and December 31, 2022, respectively	1,343,000	1,342,000
Additional paid-in capital	566,040,000	565,541,000
Accumulated deficit	(548,577,000)	(547,636,000)
Total stockholders’ equity	18,806,000	19,247,000
Total liabilities and stockholders’ equity	$ 19,299,000	$ 19,836,000

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	30,000,000	30,000,000
Common stock, shares issued	14,321,000	14,215,000
Common stock, shares outstanding	14,321,000	14,215,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive (Loss) Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses:
General and administrative expenses	$ 531	$ 504	$ 1,686	$ 1,567
Gain on sale of in-process research and development			(139)	(445)
Total operating expenses	531	504	1,547	1,122
Loss from operations	(531)	(504)	(1,547)	(1,122)
Other income:
Interest income	252	62	606	70
Total other income	252	62	606	70
Net loss and comprehensive loss	$ (279)	$ (442)	$ (941)	$ (1,052)
Net loss per common share - basic	$ (0.02)	$ (0.03)	$ (0.07)	$ (0.08)
Net loss per common share - diluted	$ (0.02)	$ (0.03)	$ (0.07)	$ (0.08)
Weighted-average common shares used to compute basic net loss per common share	14,321	13,410	14,289	13,410
Weighted-average common shares used to compute diluted net loss per common share	14,321	13,410	14,289	13,410

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2021	$ 14,187	$ 1,334	$ 558,945	$ (546,092)
Balance (in shares) at Dec. 31, 2021		13,410,000
Stock-based compensation	20		20
Net loss	(132)			(132)
Balance at Mar. 31, 2022	14,075	$ 1,334	558,965	(546,224)
Balance (in shares) at Mar. 31, 2022		13,410,000
Balance at Dec. 31, 2021	$ 14,187	$ 1,334	558,945	(546,092)
Balance (in shares) at Dec. 31, 2021		13,410,000
Number of options exercised	0
Net loss	$ (1,052)
Balance at Sep. 30, 2022	13,189	$ 1,334	558,999	(547,144)
Balance (in shares) at Sep. 30, 2022		13,410,000
Balance at Mar. 31, 2022	14,075	$ 1,334	558,965	(546,224)
Balance (in shares) at Mar. 31, 2022		13,410,000
Stock-based compensation	17		17
Net loss	(478)			(478)
Balance at Jun. 30, 2022	$ 13,614	$ 1,334	558,982	(546,702)
Balance (in shares) at Jun. 30, 2022		13,410,000
Number of options exercised	0
Stock-based compensation	$ 17		17
Net loss	(442)			(442)
Balance at Sep. 30, 2022	13,189	$ 1,334	558,999	(547,144)
Balance (in shares) at Sep. 30, 2022		13,410,000
Balance at Dec. 31, 2022	19,247	$ 1,342	565,541	(547,636)
Balance (in shares) at Dec. 31, 2022		14,215,000
Exercise of stock options	179	$ 1	178
Number of options exercised		40,000
Stock-based compensation	17		17
Net loss	(271)			(271)
Balance at Mar. 31, 2023	19,172	$ 1,343	565,736	(547,907)
Balance (in shares) at Mar. 31, 2023		14,255,000
Balance at Dec. 31, 2022	19,247	$ 1,342	565,541	(547,636)
Balance (in shares) at Dec. 31, 2022		14,215,000
Net loss	(941)
Balance at Sep. 30, 2023	18,806	$ 1,343	566,040	(548,577)
Balance (in shares) at Sep. 30, 2023		14,321,000
Balance at Mar. 31, 2023	19,172	$ 1,343	565,736	(547,907)
Balance (in shares) at Mar. 31, 2023		14,255,000
Exercise of stock options	209		209
Number of options exercised		66,000
Stock-based compensation	47		47
Net loss	(391)			(391)
Balance at Jun. 30, 2023	$ 19,037	$ 1,343	565,992	(548,298)
Balance (in shares) at Jun. 30, 2023		14,321,000
Number of options exercised	0
Stock-based compensation	$ 48		48
Net loss	(279)			(279)
Balance at Sep. 30, 2023	$ 18,806	$ 1,343	$ 566,040	$ (548,577)
Balance (in shares) at Sep. 30, 2023		14,321,000

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities
Net loss	$ (941)	$ (1,052)
Adjustments to reconcile net loss to net cash used in operating activities
Gain on sale of in-process research and development	(139)	(445)
Accretion on short-term investments	(165)
Stock-based compensation expense	112	54
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1)	(57)
Accounts payable, accrued expenses and other	(96)	(114)
Other assets	3	57
Net cash used in operating activities	(1,227)	(1,557)
Cash flows from investing activities
Net proceeds from sale of in process research and development	139	445
Proceeds from maturity of short-term investment	3,000
Purchases of short-term investments	(15,656)
Net cash (used in) provided by investing activities	(12,517)	445
Cash flows from financing activities
Proceeds from exercise of stock options	388
Net cash provided by financing activities	388
Net decrease in cash and cash equivalents	(13,356)	(1,112)
Cash and cash equivalents, beginning of period	19,439	14,203
Cash and cash equivalents, end of period	$ 6,083	$ 13,091

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Merrimack Pharmaceuticals, Inc. (the “Company”) is a biopharmaceutical company based in Cambridge, Massachusetts that is entitled to receive up to $ 450.0 million in contingent milestone payments related to its sale of ONIVYDE ® and MM-436 (the “Commercial Business”) to Ipsen S.A. (“Ipsen”) in April 2017 (the “Ipsen Sale”). The Company does not have any ongoing research or development activities. The Company does not have any employees and instead uses external consultants for the operation of the Company. The $ 450.0 million in contingent milestone payments resulting from the Ipsen Sale consist of: • $ 225.0 million upon approval by the U.S. Food and Drug Administration (“FDA”) of ONIVYDE ® for the first-line treatment of metastatic pancreatic ductal adenocarcinoma (“mPDAC”), subject to certain conditions; • $ 150.0 million upon approval by the FDA of ONIVYDE ® for the treatment of small-cell lung cancer after failure of first-line chemotherapy; and • $ 75.0 million upon approval by the FDA of ONIVYDE ® for an additional indication unrelated to those described above. In June 2023, Ipsen announced that the U.S. Food and Drug Administration (FDA) had accepted its supplemental new drug application (sNDA) Onivyde® (irinotecan liposome injection) plus 5 fluorouracil/leucovorin and oxaliplatin (NALIRIFOX regimen) as a potential first-line treatment for mPDAC and that the FDA had provided a Prescription Drug User Fee Act expected goal date of February 13, 2024 for review of the application. On May 30, 2019, the Company announced the completion of its review of strategic alternatives, following which the Company’s board of directors (the “Board”) implemented a series of measures designed to extend the Company’s cash runway and preserve its ability to capture the potential milestone payments resulting from the Ipsen Sale. In connection with that announcement, the Company discontinued the discovery efforts on its remaining preclinical programs: MM-401, an agonistic antibody targeting a novel immuno-oncology target, TNFR2; and MM-201, a highly stabilized agonist-Fc fusion protein targeting death receptors 4 and 5. The Company’s termination of its executive management team and all other employees was substantially completed by June 28, 2019 and fully completed by July 12, 2019. As of July 12, 2019, the Company no longer had any employees. The Company has engaged external consultants to run the day-to-day operations of the Company. The Company has also entered into consulting agreements with certain former members of its executive management team who are supporting the Company’s relationship with current partners, assisting with the potential sale of remaining preclinical and clinical assets, and assisting with certain legal and regulatory matters and the continued wind-down of operations. On July 12, 2019, the Company completed the sale to Elevation Oncology, Inc. (formerly known as 14ner Oncology, Inc.) (“Elevation”) of its anti-HER3 antibody programs, MM-121 (seribantumab) and MM-111 (the “Elevation Sale”). In connection with the Elevation Sale, the Company received an upfront cash payment of $ 3.5 million. The Company is also eligible to receive up to $ 54.5 million in additional potential development, regulatory approval and commercial-based milestone payments, consisting of: • $ 3.0 million for achievement of the primary endpoint in the first registrational clinical study of either MM-121 or MM-111; • Up to $ 16.5 million in total payments for the achievement of various regulatory approval and reimbursement-based milestones in the United States, Europe and Japan; and • Up to $ 35.0 million in total payments for achieving various cumulative worldwide net sales targets between $100.0 million and $ 300.0 million for MM-121 and MM-111. In January 2023, Elevation announced it is pausing further investment in the clinical development of seribantumab and intends to pursue further development only in collaboration with a partner. On September 15, 2021, the Company entered into an Asset Purchase Option Agreement (the "Asset Purchase Option Agreement") with a third party, pursuant to which the third party agreed to obtain an exclusive option, to purchase one of the Company’s preclinical programs with a consideration of $ 0.5 million. Under the terms of the Asset Purchase Option Agreement, the third party paid to the Company the option fee of $ 0.1 million. The third party had the right to exercise the option within 24 months from September 15, 2021. The Company recognized a gain of $ 0.1 million related to the option fee payment for the year ended December 31, 2021. On January 18, 2022, the third party provided written notice to the Company of its intent to exercise such option. On March 1, 2022 the Company and the third party entered into the Asset Purchase Agreement. The consideration of $ 0.5 million was paid to the Company and a net gain of $ 0.4 million was recognized in March 2022. On January 23, 2023, the Company entered into another Asset Purchase Option Agreement (the “Option Agreement”) with another third party (the “Purchaser”), pursuant to which the Purchaser agreed to obtain an exclusive option (the “Option”) to purchase one of the Company’s preclinical programs with a consideration of $ 0.7 million. Under the terms of the Option Agreement, the Purchaser paid to the Company the Option fee of $ 0.2 million and the Company incurred transaction costs less than $ 0.1 million. A net gain of $ 0.1 million was recognized in January 2023. The Purchaser decided not to exercise the Option in July 2023 . Our remaining non-commercial assets, including our clinical and preclinical development programs, and all material other clinical and pre-clinical development programs have been sold with the exception of one program. The Company is not developing and commercializing products. The Company expects to dividend out to its stockholders all or substantially all of any milestone payments it may receive and the Company does do not anticipate seeking to develop any new products with any of our existing cash or any future milestone payments it may receive. The Company’s failure to achieve these potential milestone payments would depress the value of the Company. A decline in the value of the Company could also cause its stockholders to lose all or part of their investment. The Company is subject to risks and uncertainties common to companies in the biopharmaceutical industry, including, among other things, its ability to secure additional capital to fund operations, development by competitors of new technological innovations, protection of proprietary technology and compliance with government regulations. None of the Company’s product candidates sold to others or retained by the Company are approved for any indication by the FDA or any other regulatory agency. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies, among others. In addition, the Company is dependent upon the services of its external consultants for the operation of the Company. The Company’s business strategy depends substantially upon its ability to receive future milestone payments from Ipsen. Any failure to achieve such milestones or a perception that the milestones may not be achieved will materially and adversely affect the Company and the value of its common stock. In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern , the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the condensed consolidated financial statements are issued. As of September 30, 2023, the Company had an accumulated deficit of $ 548.6 million. During the nine months ended September 30, 2023, the Company incurred a net loss of $ 0.9 million and used $ 1.2 million of cash in operating activities. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash and cash equivalents and short-term investment of $ 18.9 million at September 30, 2023 will allow the Company to continue its operations into 2027, which the Company estimates is beyond the latest date that the longest-term potential Ipsen milestone may be achieved. The continued viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations or to reduce operating expenses. There can be no assurance that the Company will be able to obtain sufficient capital to cover its costs on acceptable terms, if at all. The Company expects that it would seek to finance any future cash needs through a combination of divestitures of its rights under the Ipsen and Elevation agreements, equity offerings and debt financings. There can be no assurance as to the timing, terms or consummation of any divestiture or financing, and the terms of any such financing may adversely affect the holdings or the rights of the Company’s stockholders or require the Company to relinquish rights to certain of its revenue streams or product candidates.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements reflect the operations of Merrimack Pharmaceuticals, Inc. and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated. The condensed consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 1 to the financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 . Unaudited Interim Financial Information The condensed consolidated balance sheet as of December 31, 2022 was derived from audited financial statements for the year ended December 31, 2022, but the condensed consolidated balance sheet in this Form 10-Q at December 31, 2022 does not include all disclosures required by GAAP. The condensed consolidated balance sheet as of September 30, 2023, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2023 and 2022, the condensed consolidated statements of stockholders’ equity for the three and nine months ended September 30, 2023 and 2022 and the condensed consolidated statements of cash flows for the nine months ended September 30, 2023 and 2022 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2023, the results of its operations for the three and nine months ended September 30, 2023 and 2022, its statements of stockholders’ equity for the three and nine months ended September 30, 2023 and 2022 and its statements of cash flows for the nine months ended September 30, 2023 and 2022. The financial data and other information disclosed in the notes related to the three and nine months ended September 30, 2023 and 2022 are unaudited. The results for the three and nine months ended September 30, 2023 and 2022 are not necessarily indicative of results to be expected for the year ending December 31, 2023, any other interim periods, or any future year or period. The unaudited interim financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 filed with the SEC on March 9, 2023. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates, assumptions and judgments reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments The following tables show assets measured at fair value on a recurring basis as of September 30, 2023 and December 31, 2022: September 30, 2023 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 5,725 $ — $ — Totals $ 5,725 $ — $ — Short-term investments: Treasury bills and notes $ — $ 12,821 $ — Totals $ — $ 12,821 $ — December 31, 2022 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 18,148 $ — $ — Totals $ 18,148 $ — $ — There were no liabilities measured at fair value on a recurring basis as of September 30, 2023 and December 31, 2022. The following table summarizes the carrying values and fair values of the Company's financial instruments: September 30, 2023 (in thousands) Amortized Allowance for Credit Losses Net Carrying Amount Gross Unrealized Gross Unrealized Fair Short-term investments: Treasury bills and note $ 12,821 $ — $ 12,821 $ — $ — $ 12,821 Total short-term investments $ 12,821 $ — $ 12,821 $ — $ — $ 12,821 As of December 31, 2022, the Company did no t hold any short-term investments. The Company has investments in U.S. Treasury Bills and U.S. Treasury Notes as of September 30, 2023, some of which mature over a period greater than 90 days but within one year and are classified as short-term investments. The U.S. Treasury Bills and U.S. Treasury Notes are carried at amortized cost and classified as held to maturity as the Company has the intent and the ability to hold them until they mature. The carrying value of the U.S. Treasury Bills and U.S. Treasury Notes are adjusted for accretion of discounts over the remaining life of the investment. Income related to the U.S. Treasury Bills and U.S. Treasury Notes is recognized in interest income in the Company’s condensed consolidated statement of operations.

Accounts Payable, Accrued Expen

Accounts Payable, Accrued Expenses and Other	9 Months Ended
	Sep. 30, 2023
Payables and Accruals [Abstract]
Accounts Payable, Accrued Expenses and Other	4. Accounts Payable, Accrued Expenses and Other Accounts payable, accrued expenses and other as of September 30, 2023 and December 31, 2022 consisted of the following: (in thousands) September 30, December 31, Accounts payable $ 111 $ 188 Accrued goods and services 144 139 Accrued clinical trial costs 47 71 Others 191 191 Total accounts payable, accrued expenses and other $ 493 $ 589

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	5. Stock-Based Compensation On April 15, 2021, the Company’s Board of Directors adopted the 2021 Incentive Award Plan (the “2021 Plan”) to replace the 2011 Stock Incentive Plan (the “2011 Plan”). The 2021 Plan was approved by the Company’s stockholders at the Company’s Annual Meeting of Stockholders held on June 10, 2021. The 2021 Plan is administered by the Company’s Board of Directors and permits the Company to grant incentive and non-qualified stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. There were 22,000 options granted during each of the nine months ended September 30, 2023 and 2022 under the 2021 Plan. At September 30, 2023 , there were 209,000 shares remaining available for grant under the 2021 Plan. The aggregate intrinsic value was calculated as the difference between the exercise price of the stock options and the fair value of the underlying common stock. The aggregate intrinsic value of options exercised during the nine months ended September 30, 2023 is $ 0.9 million. There were no options exercised during the three months ended September 30, 2023 and the three and nine months ended September 30, 2022. The Company recognized stock-based compensation expense of $ 48 thousand and $ 112 thousand for the three and nine months ended September 30, 2023 , respectively, and $ 17 thousand and $ 54 thousand for the three and nine months ended September 30, 2022 , respectively, which are included in general and administrative expense on the accompanying condensed consolidated statement of operations and comprehensive loss.

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Net Loss Per Common Share	6. Net Loss Per Common Share Basic net loss per share is calculated by dividing the net loss attributable to Merrimack Pharmaceuticals, Inc. by the weighted-average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing the net loss attributable to Merrimack Pharmaceuticals, Inc. by the weighted-average number of dilutive common shares outstanding during the period. Dilutive shares outstanding is calculated by adding to the weighted shares outstanding any potential (unissued) shares of common stock from outstanding stock options based on the treasury stock method. Outstanding stock options were not included in the diluted net loss per share calculation because the options were out of the money or to do so would have been antidilutive (i.e., the total proceeds upon exercise would have exceeded the market value of the underlying common shares). In a period when a net loss is reported, all common stock equivalents are excluded from the calculation because they would have an anti-dilutive effect, meaning the loss per share would be reduced. Therefore, in periods where a loss is reported, there is no difference in basic and dilutive loss per share. Stock options are excluded from the calculation of diluted loss per share because the net loss for the three and nine months ended September 30, 2023 and 2022 causes such securities to be anti-dilutive. Outstanding options excluded from the calculation of diluted loss per share for the three and nine months ended September 30, 2023 and 2022 are shown in the chart below: Three and Nine Months Ended September 30, (in thousands) 2023 2022 Outstanding options to purchase common stock 641 1,628

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2023
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	7. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that the Company adopts as of the specified effective date. Unless otherwise discussed above, the Company does not believe that the adoption of recently issued standards has or may have a material impact on the Company’s condensed consolidated financial statements or disclosures.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements reflect the operations of Merrimack Pharmaceuticals, Inc. and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated. The condensed consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 1 to the financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 .
Unaudited Interim Financial Information	Unaudited Interim Financial Information The condensed consolidated balance sheet as of December 31, 2022 was derived from audited financial statements for the year ended December 31, 2022, but the condensed consolidated balance sheet in this Form 10-Q at December 31, 2022 does not include all disclosures required by GAAP. The condensed consolidated balance sheet as of September 30, 2023, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2023 and 2022, the condensed consolidated statements of stockholders’ equity for the three and nine months ended September 30, 2023 and 2022 and the condensed consolidated statements of cash flows for the nine months ended September 30, 2023 and 2022 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2023, the results of its operations for the three and nine months ended September 30, 2023 and 2022, its statements of stockholders’ equity for the three and nine months ended September 30, 2023 and 2022 and its statements of cash flows for the nine months ended September 30, 2023 and 2022. The financial data and other information disclosed in the notes related to the three and nine months ended September 30, 2023 and 2022 are unaudited. The results for the three and nine months ended September 30, 2023 and 2022 are not necessarily indicative of results to be expected for the year ending December 31, 2023, any other interim periods, or any future year or period. The unaudited interim financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 filed with the SEC on March 9, 2023.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of expenses during the reporting periods. Significant estimates, assumptions and judgments reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Recent Accounting Pronouncements	From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that the Company adopts as of the specified effective date. Unless otherwise discussed above, the Company does not believe that the adoption of recently issued standards has or may have a material impact on the Company’s condensed consolidated financial statements or disclosures.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on a Recurring Basis	The following tables show assets measured at fair value on a recurring basis as of September 30, 2023 and December 31, 2022: September 30, 2023 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 5,725 $ — $ — Totals $ 5,725 $ — $ — Short-term investments: Treasury bills and notes $ — $ 12,821 $ — Totals $ — $ 12,821 $ — December 31, 2022 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 18,148 $ — $ — Totals $ 18,148 $ — $ —
Summary of Carrying Values and Fair Values of Financial Instruments	The following table summarizes the carrying values and fair values of the Company's financial instruments: September 30, 2023 (in thousands) Amortized Allowance for Credit Losses Net Carrying Amount Gross Unrealized Gross Unrealized Fair Short-term investments: Treasury bills and note $ 12,821 $ — $ 12,821 $ — $ — $ 12,821 Total short-term investments $ 12,821 $ — $ 12,821 $ — $ — $ 12,821

Accounts Payable, Accrued Exp_2

Accounts Payable, Accrued Expenses and Other (Tables)	9 Months Ended
	Sep. 30, 2023
Payables and Accruals [Abstract]
Schedule of Accounts Payable, Accrued Expenses and Other	Accounts payable, accrued expenses and other as of September 30, 2023 and December 31, 2022 consisted of the following: (in thousands) September 30, December 31, Accounts payable $ 111 $ 188 Accrued goods and services 144 139 Accrued clinical trial costs 47 71 Others 191 191 Total accounts payable, accrued expenses and other $ 493 $ 589

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Outstanding Options Excluded from Computation of Diluted Loss Per Share	Outstanding options excluded from the calculation of diluted loss per share for the three and nine months ended September 30, 2023 and 2022 are shown in the chart below: Three and Nine Months Ended September 30, (in thousands) 2023 2022 Outstanding options to purchase common stock 641 1,628

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) - USD ($)			1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 23, 2023	Sep. 15, 2021	Mar. 31, 2022	Jul. 12, 2019	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2021	Dec. 31, 2022	Apr. 03, 2017
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit					$ 548,577,000		$ 548,577,000			$ 547,636,000
Net loss from continuing operations					279,000	$ 442,000	941,000	$ 1,052,000
Cash used in operating activities							1,227,000	$ 1,557,000
Cash and cash equivalents and short-term investment					$ 18,900,000		$ 18,900,000
Asset Purchase Option Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Gain related to option fee payment	$ 100,000								$ 100,000
Terms of exercise option	The Purchaser decided not to exercise the Option in July 2023
Asset Purchase Option Agreement [Member] | Pegascy SAS [Member]
Summary Of Significant Accounting Policies [Line Items]
Consideration receivable	$ 700,000	$ 500,000
Option fee	200,000	$ 100,000
Consideration received			$ 500,000
Net gain related to payment of consideration			$ 400,000
Exercise period of option		24 months
Asset Purchase Option Agreement [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Transaction expenses	$ 100,000
Ipsen [Member] | Asset Sale Agreement [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable											$ 450,000,000
Ipsen [Member] | First Line Treatment of Metastatic Pancreatic Ductal Adenocarcinoma [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable											225,000,000
Ipsen [Member] | After Failure of First Line Chemotherapy [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable											150,000,000
Ipsen [Member] | Additional Indication [Member]
Summary Of Significant Accounting Policies [Line Items]
Contingent milestone payments receivable											$ 75,000,000
14ner Sale [Member]
Summary Of Significant Accounting Policies [Line Items]
Upfront cash payment received				$ 3,500,000
14ner Sale [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events				54,500,000
14ner Sale [Member] | Achievement of the Primary Endpoint in the First Registrational Clinical Study of Either MM-121 or MM-111 [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events				3,000,000
14ner Sale [Member] | Achievement of Various Regulatory Approval and Reimbursement-Based Milestones in the United States, Europe and Japan [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events				16,500,000
14ner Sale [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Additional payments receivable on achievement of certain milestone events				35,000,000
Cumulative worldwide net sales target				$ 300,000,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Assets Measured at Fair Value on a Recurring Basis (Detail) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 12,821,000	$ 0
Recurring Basis [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	5,725,000	18,148,000
Recurring Basis [Member] | Level 1 [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	5,725,000	$ 18,148,000
Recurring Basis [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	12,821,000
Recurring Basis [Member] | Level 2 [Member] | Treasury Bills and Notes [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 12,821,000

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Short-term investments	$ 12,821,000	$ 0
Recurring Basis [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	$ 0	$ 0

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Summary of Carrying Values and Fair Values of Financial Instruments (Detail) $ in Thousands	Sep. 30, 2023 USD ($)
Schedule of Held-to-Maturity Securities [Line Items]
Short-term investments, Amortized Cost	$ 12,821
Short-term investments, Net Carrying Amount	12,821
Short-term investments, Fair Value	12,821
Treasury Bills and Note [Member]
Schedule of Held-to-Maturity Securities [Line Items]
Short-term investments, Amortized Cost	12,821
Short-term investments, Net Carrying Amount	12,821
Short-term investments, Fair Value	$ 12,821

Accounts Payable, Accrued Exp_3

Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accounts payable	$ 111	$ 188
Accrued goods and services	144	139
Accrued clinical trial costs	47	71
Others	191	191
Total accounts payable, accrued expenses and other	$ 493	$ 589

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of options exercised			$ 900
Number of options exercised	0	0		0
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	$ 48	$ 17	$ 112	$ 54
Stock Incentive Plan 2021 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options granted			22,000	22,000
Shares of common stock available for grant (in shares)	209,000		209,000

Net Loss Per Common Share - Sch

Net Loss Per Common Share - Schedule of Outstanding Options Excluded from Computation of Diluted Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Outstanding Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding options to purchase common stock	641	1,628	641	1,628