Biogen Increases Sample Size for Alzheimer’s Phase 3; Stock Takes a Dip


Biogen has decided to add 510 patients its upcoming phase 3 aducanumab trails because they didn’t expect to have so much variability in a sample size re-estimation. The midstudy changes to its Alzheimer’s program had scared its investors.

Speculations about the drug took a toll on its shares as Biogen dropped as much as 9 percent.

The chief of marking for the company, Al Sandrock, made a point in saying, “We did do a preplanned blinded sample size re-estimation. We did see more variability in the primary endpoint than assumed when we did the original sample size estimation, so we decided to increase the sample size to maintain 90% power. Therefore, we’re going to add 510 patients to the two studies”.

Sandrock was strategic in addressing the changes made to the trial and made them seem minor. Biogen wants people to view the re-estimation as nothing more than a protocol, and that the company has applied this same strategy to other drugs. This is to reassure people and investors that there is nothing to worry about, and the success of aducanumab has nothing to do with the increased sample size. The drug is still on track for enrollment by this summer.

Sandrock continued to speak about the drug by saying that very few patients have dropped out of the study. They expected more to drop out and therefore their prediction for dropout rate was incorrect, but besides this everything is moving as expected.

Regardless of the positive statement made by Sandrock, nothing could mask the change in sample size as it was recently released at a conference. This blindsided investors completely, and as a result the stock crashed. Biogen’s ability to be successful has really come into question with this new drug.

Analysts, like Micheal Yee, believe that Biogen should refocus some of the statements they are making about how this new drug is vital to the future success of the company.

Yee wrote to investors saying, “While we maintain a positive stance on data in 2020, we think [Biogen] needs to go out and buy derisked neuro/orphan companies to “change the narrative” to being a binary Alzheimer’s company to one with products even if Alzheimer’s doesn’t work.”


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