Mersana Therapeutics (NASDAQ:MRSN) stock plummeted more than 60% on Thursday after the clinical-stage biopharmaceutical company announced that the Food and Drug Administration (FDA) has issued a partial clinical hold pausing new patient enrollment in its ongoing clinical trials evaluating its therapeutic UpRi in platinum-sensitive ovarian cancer, UP-NEXT and UPGRADE-A.
The partial clinical hold comes after Mersana submitted aggregate safety reports of all patients dosed with UpRi, approximately 560 patients, evaluating bleeding events.
The company said, although data on the background rate of bleeding in platinum-resistant ovarian cancer are limited, its recent assessment determined that serious bleeding events appear to occur at a higher rate than the background.
Most bleeding cases in the aggregate safety analysis were low-grade and five were Grade 5 (fatal) bleeding events, Mersana reported.
The cause of the bleeding events is under investigation, it added.
“Patient safety is always at the forefront for us, and work is now underway to compile further analyses that may inform the FDA,” said Mersana CEO Anna Protopapas.
The company added that it expects topline data from its UPLIFT trial of UpRi in platinum-sensitive ovarian cancer in early August.
“With UPLIFT top-line data on the near-term horizon, we will soon have a much more complete assessment of both the efficacy and safety profile for UpRi in platinum-resistant ovarian cancer,” Protopapas said.
Mersana shares were down 60.4% at US$3.79 shortly after the opening bell in New York on Thursday.
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