A spokesperson for the Japanese drugmaker confirmed there was a third death in a clinical trial of the experimental treatment lecanemab. The company is currently investigating the cause of it.

Science Insider earlier reported a 79-year-old Florida woman in a trial of the antibody treatment died in mid-September after experiencing swelling and bleeding in the brain and seizures.

Eisai shares were down 3.9% as of 1:43 p.m. in Tokyo (0443 GMT), versus a 0.9% drop in the benchmark Nikkei index.

Shares in Eisai and U.S. partner Biogen Inc have been whipsawed for years on the prospects of their experimental treatments for the brain-wasting disease that affects millions across the globe.

After a previous death in the lecanemab trial, some analysts said it was not clear if use of the drug was raising the risk of bleeding, and cautioned against concurrent use of blood thinners.

Eisai plans to seek full approval of the drug in the United States, Europe and Japan next year.

Earlier on Friday, the company said it submitted data on lecanemab for a Biologics License Application (BLA) in China.

(Reporting by Rocky Swift and Mariko Katsumura)