Share of Biogen (BIIB) - Get Report   rose Friday after the company announced that it was cancelling two late stage trials testing its experimental Alzheimer's treatment, elenbecestat. 

The treatment is being co-developed with Eisai (ESALY)  . The companies said the decision to end the trials was based off results of a safety review conducted by a data safety monitoring board, which recommended an end to the trials due to an unfavorable risk-benefit ratio. 

"We are very disappointed with the news, and intend to learn from these data and continue engaging with patients and investigators, to pursue the discovery of new medicines for Alzheimer's disease, said Dr. Lynn Kramer, chief clinical officer, neurology business group, Eisai.

About 2,100 patients with mild cognitive impairment or mild Alzheimer's disease took part in the placebo-controlled, double-blind tests. The patients were randomized to receive either 50 mg of elenbecestat or a placebo daily during the treatment period of 24 months. 

Biogen shares climbed 0.51% in premarket trading Friday to $233.50.