TOKYO, Nov 29 (Reuters) - Shares in Japanese drugmaker Eisai Co headed for their biggest plunge in more than a year on Tuesday after a report that a woman in a trial of the company's Alzheimer's disease treatment died.

A woman receiving lecanemab, an experimental drug developed by Eisai and its U.S. partner Biogen Inc, recently died from a brain haemorrhage, research paper publisher Science.org reported on Sunday.

That would mark a second fatality in a lecanemab trial, following the death of a man in his 80s in June, according to a report by the health journal STAT.

Eisai's shares sank 10% to 8,595 yen, leading decliners on the benchmark Nikkei index, which slid 0.5% in the morning session. Shares in Biogen sank 4.3% on Monday.

Eisai, in response to a request for comment on the report, said it cannot provide any information about specific patients or comment on information that was provided by other sources. Biogen did not immediately respond to a request for comment.

Eisai and Biogen shares have been on a roller coaster in recent years on prospects for their candidates to battle dementia.

The companies' previous drug Aduhelm won approval from the U.S. Food and Drug Administration in 2021, but its use has been limited due to concerns over its price and effectiveness.

Lecanemab was shown to slow cognitive and functional decline in a large trial of patients in the early stages of Alzheimer's disease, Eisai and Biogen said in September. (Reporting by Rocky Swift in Tokyo and Raghav Mahobe and Khushi Mandowara in Bengaluru; Editing by Cynthia Osterman)