Why Merrimack Pharmaceuticals (MACK) Stock is Down in After-Hours Trading Today

NEW YORK (TheStreet) -- Merrimack Pharmaceuticals  (MACK) fell in after-hours trading on Thursday after the company announced it had regained worldwide rights from Sanofi  (SNY) to develop and commercialize MM-121.

MM-121 is "a monoclonal antibody designed to block ErbB3 (HER3) activation in patients with heregulin-positive tumors and improve response to standard of care treatments," according to the company's press release.

The rights acquisition ends Merrimack's five-year partnership with Sanofi, which helped Merrimack complete a Phase 2 program for MM-121. Sanofi will continue to fund the program for the next six months.

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The stock was down 9.13% to $7.17 at 4:45 p.m.

MACK Price Chart

MACK Price data by YCharts

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