May 5, 2015

Merrimack Pharmaceuticals Announces Initiation of a Phase 2 Front-line Clinical Trial of MM-141 in Biomarker-Selected Patients with Metastatic Pancreatic Cancer

Trial is enrolling prospectively selected patients with high serum levels of free IGF-1, a tumor-binding protein that drives tumor growth and resistance

CAMBRIDGE, Mass., May 5, 2015 /PRNewswire/ -- Merrimack Pharmaceuticals, Inc. (Nasdaq: MACK) today announced the initiation of a randomized, double-blinded, placebo-controlled Phase 2 clinical trial of MM-141, a bispecific antibody targeting IGF-1R and ErbB3, in combination with nab-paclitaxel and gemcitabine, versus nab-paclitaxel and gemcitabine alone in patients with newly-diagnosed metastatic pancreatic cancer who have high serum levels of free IGF-1.

"Pancreatic cancer is the fourth leading cause of cancer death in the United States and is projected to rise to the second leading cause by 2020. Merrimack is committed to advancing the standard of care for patients with inoperable, metastatic pancreatic cancer. We are taking steps to move our therapeutics forward based on matching them to the biology of individual tumors," said Chrystal Louis, M.D., Medical Director of MM-141 at Merrimack. "Data from our Phase 1 trial supports further clinical evaluation of MM-141 in patients with high serum levels of free IGF-1. Patients with this biomarker profile may have the greatest potential of benefit from the use of MM-141 combined with standard chemotherapies, and we look forward to further validating this in our Phase 2 trial."

As part of this trial, 146 front-line metastatic pancreatic cancer patients with high serum levels of free IGF-1 will be randomized (1:1) to receive either MM-141 plus nab-paclitaxel/gemcitabine or nab-paclitaxel/gemcitabine alone. Eligible patients for the trial must have received no prior radiotherapy, surgery, chemotherapy or investigational therapy for the treatment of metastatic disease. The primary endpoint of the trial is progression free survival (PFS). Secondary endpoints include overall survival, objective response rate, safety and tolerability. Merrimack plans to conduct the trial at sites in the United States, Canada and Europe. Initial trial sites located at St. Jude Heritage in Fullerton, California and Northwestern University in Chicago, Illinois are now open to screen patients in the United States.  For more information, please visit (Identifier: NCT02399137).

About MM-141

MM-141 is a tetravalent bispecific antibody designed to block tumor survival signals by targeting receptor complexes containing IGF-1R and ErbB3 (HER3). IGF-1R and ErbB3 complexes both activate a major signaling pathway that allows tumor cells to grow and develop resistance to chemotherapy. MM-141 has been tested in a Phase 1 dose-escalation clinical trial. The U.S. Food and Drug Administration (FDA) has granted orphan drug designation for MM-141 for the treatment of pancreatic cancer. This orphan drug designation could provide Merrimack with seven-year marketing exclusivity and other benefits for MM-141 when approved by the FDA.

About Merrimack

Merrimack is a biopharmaceutical company discovering, developing and preparing to commercialize innovative medicines paired with companion diagnostics for the treatment of cancer. Merrimack seeks to gain a deeper understanding of underlying cancer biology through its systems biology-based approach and develop new insights, therapeutics and diagnostics to improve outcomes for cancer patients. Merrimack has multiple oncology therapeutics in clinical development and additional candidates in late stage preclinical development. Merrimack has submitted a New Drug Application for its lead product candidate, MM-398, for the treatment of patients with metastatic adenocarcinoma of the pancreas who have been previously treated with gemcitabine-based therapy. For more information, please visit Merrimack's website at or connect on Twitter at @MerrimackPharma.

Forward-Looking Statements

To the extent that statements contained in this press release are not descriptions of historical facts, they are forward-looking statements reflecting the current beliefs and expectations of management made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include any statements about Merrimack's strategy, future operations, future financial position and future expectations and plans and prospects for Merrimack, and any other statements containing the words "anticipate," "believe," "estimate," "expect," "intend," "may," "plan," "predict," "project," "target," "potential," "will," "would," "could," "should," "continue," "hope" and similar expressions. In this press release, Merrimack's forward-looking statements include statements about the potential effectiveness and safety profile of MM-141 in certain patient populations or subpopulations, its ability to use free IGF-1 as a predictive diagnostic and its ability to translate clinical data into future clinical success.  Such forward-looking statements involve substantial risks and uncertainties that could cause Merrimack's clinical development programs, future results, performance or achievements to differ significantly from those expressed or implied by the forward-looking statements. Such risks and uncertainties include, among others, availability of data from ongoing clinical trials, expectations for regulatory approvals, development progress of Merrimack's companion diagnostics and other matters that could affect the availability or commercial potential of Merrimack's drug candidates or companion diagnostics. Merrimack undertakes no obligation to update or revise any forward-looking statements. Forward-looking statements should not be relied upon as representing Merrimack's views as of any date subsequent to the date hereof. For a further description of the risks and uncertainties that could cause actual results to differ from those expressed in these forward-looking statements, as well as risks relating to Merrimack's business in general, see the "Risk Factors" section of Merrimack's Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 27, 2015 and other reports Merrimack files with the SEC.

Media Contact:
Dana Robie

Investor Contact:
Geoffrey Grande, CFA

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SOURCE Merrimack Pharmaceuticals, Inc.

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