Mersana's cancer drug studies halted by US FDA, shares fall.

The US FDA has halted enrollment in two studies of Mersana Therapeutics' ovarian cancer drug after five deaths in bleeding-related events. The cause of the bleeding events is under investigation, but patients who are already enrolled in the studies will continue to receive the treatment. Mersana's shares fell 61.1% to $3.70 in early morning trade. The FDA is expected to ask for a comprehensive assessment of the safety data of Mersana's lead drug, upifitamab rilsodotin (UpRi).