The FDA lifts a partial hold on Mersana’s top drug — and then its shares crater

Mersana $MRSN and the FDA have come up with a newly revised development program for the biotech’s lead drug just a couple months after a patient’s death triggered a partial hold on enrolling more people for the study.

From the beginning, Mersana noted that the death may have been caused by XMT-1522, an antibody drug conjugate designed to drop a therapeutic payload on HER2-expressing tumors. 

Anna Protopapas

Quickly navigating their way through the challenge, the company came up with a plan to exclude any patient candidates with advanced hepatic impairment. Researchers are also adding a once-every-four-weeks dose regimen to compared the efficacy and safety responses in patients.

The Cambridge, MA-based biotech has kept its other clinical program on track for XMT-1536 — targeting NaPi2b — but execs say they’ll make similar changes on the parallel track. And after initially boosting the biotech’s share price, investors scrambled, sending shares down 25% Monday afternoon.

Mersana CEO Anna Protopapas saw her company’s stock take a nasty hit on the news of the partial hold earlier. Since then, the share price has been rising steadily — until today’s news came through. 

This morning the stock jumped about 8% in pre-market trading to help complete the comeback, then plunged, dropping into the red by about 25% in an abrupt turnabout.

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