Merrimack Pharmaceuticals
American biopharmaceutical company focused on cancer medicines and oncology drug development.
Last updated August 26, 2026
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Overview
Merrimack Pharmaceuticals, Inc. was an American biopharmaceutical company headquartered in Cambridge, Massachusetts, that specialized in developing medicines for cancer. Founded in 2000 by scientists associated with the Massachusetts Institute of Technology and Harvard University, the company pursued a research-driven oncology model built around targeted biologic therapies, antibody engineering, drug delivery, and molecular approaches to cancer treatment. Its pipeline included investigational programs aimed at targets such as HER2, HER3, EGFR, and IGF-1R, reflecting Merrimack’s emphasis on using tumor biology and biomarker information to guide treatment development. The company’s most important commercial achievement was Onivyde, a liposome-encapsulated formulation of irinotecan. The product received its first United States Food and Drug Administration approval in 2015 for use in previously treated metastatic pancreatic adenocarcinoma in combination with fluorouracil and leucovorin. European Union approval followed in 2016. Onivyde became the central asset in Merrimack’s commercial strategy, but the company’s financial and operational position weakened after challenges surrounding its development portfolio and the departure of senior leadership. In October 2016, chief executive Robert Mulroy resigned, and Merrimack announced a workforce reduction affecting approximately 20 percent of employees. Gary Crocker served as interim chief executive before leaving in January 2017. The board then appointed Richard Peters, a former Sanofi executive and Harvard faculty member, as president and chief executive officer. Shortly afterward, Ipsen announced an agreement to acquire rights to Onivyde from Merrimack for approximately $1 billion. The transaction materially changed Merrimack’s role: after the deal closed, the company reduced its headcount by roughly 80 percent and moved toward a substantially smaller corporate structure focused on managing remaining assets and obligations rather than building a broad commercial organization. Merrimack’s remaining clinical programs included MM-302, a HER2-targeting antibody-drug conjugate; MM-121, also known as seribantumab, an anti-HER3 monoclonal antibody; MM-141, also known as istiratumab, a bispecific antibody directed at IGF-1R and HER3; and MM-151, a mixture of anti-EGFR monoclonal antibodies. These programs illustrate the company’s historical focus on targeted oncology, although the available reference material does not establish that all of them reached commercialization or remained active through the company’s final period. The company also faced legal and regulatory scrutiny connected with former employee Songjiang Wang, who was convicted in 2018 of securities fraud and conspiracy to commit securities fraud and later faced an insider-trading charge from the United States Securities and Exchange Commission. This matter concerned an individual associated with Merrimack rather than a marketed medicine or a stated company product policy. In May 2024, Merrimack stockholders approved a plan of dissolution at a special meeting. The board declared a liquidating cash dividend of $15.10 per share, with payment expected around May 17, 2024. Merrimack’s common stock continued trading on Nasdaq through May 17 and was scheduled to be delisted on May 20. These actions marked the end of the company as an operating publicly traded biopharmaceutical enterprise.
History
Merrimack Pharmaceuticals was established in 2000 by a group of scientists from MIT and Harvard. From its Cambridge base, the company developed an oncology-focused research platform combining molecular biology, antibody technologies, and drug-delivery approaches. Its programs were designed to address cancer pathways and tumor markers, with several candidates entering clinical development against HER2, HER3, EGFR, and IGF-1R. The company’s first FDA-approved medicine was Onivyde, a liposome-encapsulated version of irinotecan. The FDA approved it in 2015 for a pancreatic adenocarcinoma indication, and the European Union authorized it the following year. Onivyde was the company’s principal commercial asset and became the subject of a major transaction with Ipsen in 2017. Ipsen announced an agreement to purchase Onivyde from Merrimack for approximately $1 billion. Merrimack’s organization contracted sharply during this period. In October 2016, CEO Robert Mulroy resigned, and the company announced a workforce reduction of about 20 percent. Interim CEO Gary Crocker subsequently left in January 2017, when Richard Peters was appointed president and CEO. After the Onivyde transaction closed, Merrimack reduced its headcount by approximately 80 percent. By May 2019, the company planned to eliminate its remaining staff, including its leadership team, indicating that it had moved away from operating as a conventional fully staffed drug-development company. The company’s clinical pipeline included MM-302, a HER2-targeting antibody-drug conjugate; MM-121 or seribantumab, an anti-HER3 monoclonal antibody; MM-141 or istiratumab, a bispecific antibody directed at IGF-1R and HER3; and MM-151, an anti-EGFR antibody mixture. The available reference material does not provide sufficient information to establish the final clinical or commercial outcomes of each program. Merrimack was also associated with a securities case involving Songjiang Wang, its statistical programming director. Wang was convicted in 2018 of securities fraud and conspiracy to commit securities fraud and received a six-month prison sentence with supervised release. In 2019, the SEC separately charged him with insider trading. In 2024, the company entered its final dissolution process. On May 10, stockholders approved a plan of dissolution at a special meeting. The board declared a liquidating dividend of $15.10 per share, expected to be paid around May 17. Merrimack’s common stock continued trading on Nasdaq through May 17 and was scheduled to be delisted on May 20, completing the transition from a public biopharmaceutical company to a dissolved entity.
- 2024
Plan of dissolution approved
[1]Stockholders approve a plan of dissolution and the company declares a liquidating dividend before Nasdaq delisting.
- 2017
Onivyde transaction with Ipsen
[1]Ipsen announces an agreement to acquire Onivyde from Merrimack for approximately $1 billion.
- 2016
European Union approval for Onivyde
[1]Onivyde receives authorization in the European Union for pancreatic adenocarcinoma.
- 2015
First FDA-approved medicine
[1]Onivyde becomes Merrimack’s first medicine approved by the United States Food and Drug Administration.
- 2000
Merrimack is founded
[1]Scientists from MIT and Harvard establish Merrimack as an oncology-focused biopharmaceutical company.
Products and positioning
A research-led oncology biopharmaceutical company focused on targeted cancer therapies, biologic medicines, and specialized drug-delivery technologies.
Oncology medicine · 2015
Onivyde
Onivyde is a liposome-encapsulated formulation of irinotecan developed for cancer treatment. It became Merrimack’s first FDA-approved product in 2015 and was approved in the European Union in 2016. Its principal referenced use was in pancreatic adenocarcinoma, where it was used in combination with fluorouracil and leucovorin after prior treatment. Merrimack later transferred the asset to Ipsen in a transaction announced in 2017.
Antibody-drug conjugate
MM-302
MM-302 was an investigational antibody-drug conjugate designed to target HER2. The program represented Merrimack’s strategy of combining antibody-based tumor targeting with a cytotoxic payload. The available reference material identifies it as a clinical-development program but does not specify a commercial launch or final development outcome.
Monoclonal antibody
MM-121 (seribantumab)
MM-121, also known as seribantumab, was an investigational monoclonal antibody directed against HER3. It was part of Merrimack’s targeted oncology pipeline and reflected the company’s interest in blocking receptor signaling associated with tumor growth. The available source does not establish a commercial launch or the program’s final disposition.
Bispecific monoclonal antibody
MM-141 (istiratumab)
MM-141, also known as istiratumab, was an investigational bispecific monoclonal antibody targeting IGF-1R and HER3. Its design was intended to interfere with signaling through two receptor systems relevant to cancer biology. The referenced material lists the program among Merrimack’s clinical candidates but does not document a marketed product or definitive development result.
Monoclonal antibody mixture
MM-151
MM-151 was an investigational mixture of monoclonal antibodies directed against EGFR. It was developed as part of Merrimack’s effort to use multiple antibody components against a cancer-related receptor. The available reference material identifies MM-151 as a clinical-development program and does not provide evidence of a commercial launch or final regulatory status.
Controversies
2019
SEC insider-trading charge involving Songjiang Wang
The United States Securities and Exchange Commission charged Songjiang Wang with insider trading in a separate proceeding.
2018
Securities-fraud conviction involving Songjiang Wang
Songjiang Wang, identified as Merrimack’s statistical programming director, was convicted of securities fraud and conspiracy to commit securities fraud. A United States district court imposed a six-month prison sentence and supervised release.
Brand decisions
2024
Dissolution and liquidationOtherBackground
After its commercial and operating footprint had substantially contracted, Merrimack sought to wind down the publicly traded company.
Action taken
Stockholders approved a plan of dissolution, and the board declared a liquidating cash dividend of $15.10 per share.
Aftermath
The common stock continued trading through May 17, 2024 and was scheduled to be delisted from Nasdaq on May 20, 2024.
Liquidating cash dividend per share. $15.10 per share (May 2024)
2017
Transfer of Onivyde to IpsenM&ABackground
Onivyde was Merrimack’s first FDA-approved medicine and its principal commercial asset.
Action taken
Merrimack agreed to transfer Onivyde to French pharmaceutical company Ipsen in a transaction valued at approximately $1 billion.
Aftermath
After the deal closed, Merrimack reduced its headcount by approximately 80 percent and shifted toward a much smaller corporate structure.
Approximate transaction value. $1 billion (2017 announcement)
2016
Workforce reduction after leadership changeStrategyBackground
After CEO Robert Mulroy resigned, Merrimack reassessed its organization and announced a workforce reduction affecting approximately 20 percent of employees.
Action taken
The company announced the reduction and began operating with a smaller workforce.
Aftermath
Gary Crocker later left as interim CEO, and Richard Peters became president and CEO in January 2017.
Sources1 sources
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