Eisai shares fell the most in about 16 months following a report of a second death potentially linked to the groundbreaking experimental drug for Alzheimer’s disease it’s developing with Biogen.

The case involved a 65-year-old woman who died of a massive brain hemorrhage after suffering a stroke and a type of brain swelling and bleeding in an Eisai trial, according to a report in Science magazine. The bleeding began after the patient received an anti-clotting drug, the report said. Brain swelling and bleeding have previously been linked to medicines that work like the Biogen-Eisai treatment.

Eisai shares plunged as much as 12% in Tokyo Tuesday, the largest intraday drop since July 16 last year. Biogen fell 4.3% Monday in New York, the most since Sept. 29.