Mersana Therapeutics Inc.’s stock MRSN cratered 73% premarket Thursday, after the company announced that the U.S. Food and Drug Administration had placed a partial clinical hold on two trials of a treatment for ovarian cancer after five participants died. The agency has directed to company to pause new patient enrollment in the trials dubbed Up-Next and Upgrade-A, which are evaluating UpRi in platinum-sensitive ovarian cancer. “The partial clinical hold follows a submission by Mersana of a recent aggregate safety report of all patients dosed with UpRi (approximately 560 patients) evaluating bleeding events,” the Cambridge,…
