US FDA halts enrollment in Mersana's cancer drug studies, shares drop

New Delhi: Mersana Therapeutics said on Thursday the U.S. Food and Drug Administration (FDA) had paused enrollment in two studies of its ovarian cancer drug after five deaths in bleeding-related events, sending shares of the company tumbling.

Mersana said the cause of the bleeding events was under investigation, but patients who are already enrolled in the studies will continue to receive the treatment.

Shares of the drug developer, which had a market capitalization of $1.09 billion as of Wednesday's close, fell 61.1 per cent to $3.70 in early morning trade.

"We are admittedly surprised by the partial hold, as rates of thrombocytopenia (low blood platelet count, which causes bleeding) in prior studies have not appeared unusually high or serious," Wedbush Securities analyst David Nierengarten said.

Mersana said it expects the FDA to ask for a comprehensive assessment of the safety data of upifitamab rilsodotin (UpRi), the company's lead drug.

"Work is now underway to compile further analyses that may inform FDA," Mersana CEO Anna Protopapas said.

UpRi is also being tested in another ovarian cancer study, which has already completed enrollment, and data from it is expected in August.