Biogen is crashing after scrapping its late-stage Alzheimer's drug trials

REUTERS/Brian Snyder

A sign marks a Biogen facility in Cambridge.

• Biogen and the Japanese pharmaceutical company Eisai said Thursday they would discontinue late-stage Alzheimer's drug trials.
• Shares of Biogen crashed more than 25% in pre-market trading.
• Watch Biogen trade live.

Biogen shares crashed more than 25% in pre-market trading Thursday after the biotech company and Eisai, a Japanese pharmaceutical company, said they would discontinue two late-stage Alzheimer's drug trials.

The two companies said they would scrap their global late-stage trials, ENGAGE and EMERGE, designed to "evaluate the efficacy and safety of aducanumab in patients with mild cognitive impairment due to Alzheimer's disease and mild Alzheimer's disease dementia."

The recommendation to halt the studies was not based on safety concerns, the companies said.

"This disappointing news confirms the complexity of treating Alzheimer's disease and the need to further advance knowledge in neuroscience," Biogen CEO Michel Vounatsos said in a release. "We are incredibly grateful to all the Alzheimer's disease patients, their families and the investigators who participated in the trials and contributed greatly to this research."

Biogen's pre-market move was its largest downside gap since August 2008, when the stock traded under $50, according to Bespoke Investment Group. At the time, there were safety concerns over the future of the multiple sclerosis drug Tysabri, which Biogen and the Irish drugmaker Elan were trialing.

Biogen was up 6% this year through Wednesday.

This story is developing. Please check back for updates.

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