UPDATE 1-U.S. FDA panel votes successful study on Biogen Alzheimer's drug cannot stand alone

(Recasts first paragraph with vote on first question)

Nov 6 (Reuters) - A panel of outside advisers to the U.S. Food and Drug Administration on Friday voted that one of two large studies on Biogen Inc’s experimental Alzheimer’s disease drug cannot be viewed alone without regard for the other failed trial.

Eight members of the expert panel voted that both trials must be taken into consideration, one voted that the successful trial could stand as proof of efficacy on its own and two were uncertain.

The FDA is expected to make its approval decision by March. The drug, aducanumab, is poised to become the first new treatment for the disease in decades and the first that appears to be able to slow progression of the fatal, mind-wasting condition, should it win U.S. approval.

Biogen shares were halted ahead of the advisory panel meeting.

Alzheimer’s disease is the sixth leading cause of death in the United States and there is “a profound and enormous unmet medical need” for new treatments, Billy Dunn, director of neurology products for the FDA’s Center for Drug Evaluation and Research, said during the meeting.

Biogen in October last year revived its plans to seek approval for aducanumab, months after it had said that an independent futility analysis of its two pivotal trials showed they were unlikely to succeed.

Biogen said it changed course after a new analysis showed a high dose of the drug could slow disease progression.

The FDA staff earlier this week said data from one of the trials “provides the primary evidence of effectiveness” and a clinically meaningful treatment effect.

They said failure of a second large trial did not detract from the findings of the positive study.

The expert panel on Friday is set to vote on three other questions including whether the results from the successful study alone could be considered as the main evidence of the drug’s effectiveness in treating Alzheimer’s.

The panel will also discuss results from a third early-stage study providing supportive evidence of aducanumab’s efficacy.

The FDA is not obligated to abide by its advisory panel recommendations, but typically does.

Reporting by Manojna Maddipatla in Bengaluru; Editing by Bill Berkrot