Merrimack Pharmaceuticals, Inc. (NASDAQ:MACK) announced results from the final analysis of the Phase 1 study of MM-151, a novel investigational oligoclonal epidermal growth factor receptor (EGFR) inhibitor, in patients with refractory solid tumors. These results were presented at a Poster Discussion Session at the 2016 American Society of Clinical Oncology(ASCO) Annual Meeting in Chicago.

Data from the Phase 1 study show positive clinical activity across multiple solid tumor types in a heavily pretreated patient population. Twenty-one percent of evaluable patients in the metastatic colorectal cancer (CRC) cohort achieved an objective response and 54 percent of patients showed a decrease in tumor size. A median progression-free survival (PFS) of four months was also observed within the CRC cohort. MM-151 also exhibited positive clinical activity in both EGFR-treatment refractory and EGFR-treatment naïve populations. These preliminary data support the potential for broad clinical effect, and demonstrate an acceptable safety profile consistent with existing EGFR therapies.

“We are excited to present the final analysis of the Phase 1 data of MM-151, Merrimack’s novel oligoclonal EGFR-inhibitor,” said J. Marc Pipas, M.D., Senior Medical Director at Merrimack. “The promising preliminary Phase 1 data highlights MM-151’s ability to impair EGFR-driven signaling and overcome resistance, particularly in colorectal cancer patients. We are encouraged by these results given the unmet needs in this patient population, and we look forward to further evaluating this investigational therapy’s potential to address this challenging disease.”

CRC is the third most common cancer and is the second leading cause of cancer death in the United States. An estimated 144,000 new cases are expected to be diagnosed in 2016. The five-year survival rate for metastatic CRC is estimated at 11 percent.i The two most recent approved drugs for late stage metastatic CRC demonstrated objective response rates of less than two percent and PFS below two months in their clinical studies, while demonstrating an overall survival benefit versus best supportive care (no drug treatment)ii iii.

Methodology and Results

This study evaluated MM-151 as a monotherapy and in combination with irinotecan. An expansion cohort was enrolled to evaluate clinical activity in EGFR-refractory metastatic CRC patients. Subset analyses and additional biomarker evaluations were performed in EGFR-driven indications. A total of 111 patients were treated with escalating dose levels; 87 patients on monotherapy and 24 patients receiving MM-151 in combination with irinotecan. The most common tumor types were CRC (45 [41%]), head and neck cancers (14 [13%]) and non-small cell lung cancer (11 [10%]).

Safety of MM-151

  • MM-151 demonstrated a comparable safety profile to approved EGFR inhibitors as a monotherapy and in combination with irinotecan.
  • Apart from infusion reactions, which occurred at decreasing frequency and severity as the dosing schedule was modified over the course of the study, the most common adverse events reported were rash, hypomagnesemia, fatigue and diarrhea in the monotherapy cohorts. These adverse events were expected and consistent with EGFR inhibition class toxicities.


  • Preliminary indications of clinical activity with MM-151, across both the EGFR-refractory and naïve populations, suggest there is potential for broad effect.
  • Biomarker profiling suggests MM-151 may overcome mechanisms of resistance.
  • Preliminary data in the CRC subset show 54 percent of evaluable patients had a reduction in tumors. Forty-five percent (13/29) of patients in the CRC subset achieved stable disease or partial response at three cycles of treatment and 17 percent (5/29) achieved a partial response, with highly durable responses and disease control.
  • Preliminary biomarker analysis of blood samples (“liquid biopsies”) following MM-151 treatment show low occurrence of acquired KRAS/NRAS/BRAF mutations in the CRC cohort and no occurrence of acquired EGFR extracellular domain mutations, which have been reported to mediate resistance to cetuximab and panitumumab.
  • A median PFS of four months was observed in the CRC cohort.
  • Observations in exploratory biomarker analyses are consistent with the multiple mechanisms of action that have been previously described for MM-151 in preclinical studies, including EGFR downregulation, expression of high-affinity EGFR ligands across indications (including refractory metastatic CRC) and activity in tumors expressing EGFR and downstream mutations.
  • Further clinical evaluation is underway. (Original Source)

Shares of Merrimack Pharmaceuticals closed last Friday at $6.78, down $0.22 or -3.14%. MACK has a 1-year high of $13 and a 1-year low of $5.02. The stock’s 50-day moving average is $6.86 and its 200-day moving average is $7.21.

On the ratings front, Merrimack has been the subject of a number of recent research reports. In a report issued on May 26, Robert W. Baird analyst Michael Ulz initiated coverage with a Hold rating on MACK and a price target of $8, which represents a potential upside of 18.0% from where the stock is currently trading. Separately, on May 20, Brean Murray Carret’s Jonathan Aschoff reiterated a Buy rating on the stock and has a price target of $16.

According to, which ranks over 7,500 financial analysts and bloggers to gauge the performance of their past recommendations, Michael Ulz and Jonathan Aschoff have a total average return of -14.0% and -9.4% respectively. Ulz has a success rate of 50.0% and is ranked #3349 out of 3894 analysts, while Aschoff has a success rate of 38.0% and is ranked #3866.

Merrimack Pharmaceuticals, Inc. engages in discovering, developing and preparing to commercialize innovative medicines consisting of novel therapeutics paired with diagnostics for the treatment of cancer. Its offers its first commercial product, Onivyde, which is a novel encapsulation of the marketed chemotherapy drug irinotecan in liposomal formulation.