Biogen’s Latest Alzheimer’s Bet Didn’t Fully Succeed – But Still Sent BIIB Stock Soaring

• Biogen said the overall biomarker and efficacy data were strong enough to advance the drug into registrational development, even though the trial did not meet the primary endpoint.
• The 18-month placebo-controlled study showed strong reductions in tau levels across all doses tested.
• The treatment’s safety profile was largely consistent with earlier studies.

Shares of Biogen Inc (BIIB) surged more than 7% in pre-market trading on Tuesday, putting the stock on track for its highest level in nearly two years, after the biotech giant unveiled encouraging Phase 2 results for its experimental Alzheimer’s therapy. 

While the study missed its primary endpoint tied to dose response, Biogen said the overall biomarker and clinical efficacy package was strong enough to move the therapy into registrational development, which is a key step toward a potential U.S. Food and Drug Administration filing. 

BIIB Plans To Advance Drug To Registrational Development

Biogen conducted a Phase 2 Celia study evaluating Diranersen, a Tau-targeting treatment, in people with early-onset Alzheimer’s disease. Tau is a stabilizing protein found in the brain.

Retail sentiment for BIIB on Stocktwits turned ‘neutral’ from ‘bearish’ a day earlier, amid ‘high’ message volumes.

Why Tau-Targeting Alzheimer’s Drugs Matter

The 18-month placebo-controlled study showed strong reductions in tau levels across all doses tested, with pre-specified cognitive analyses indicating slower clinical decline, especially in patients receiving the lowest dose.

The treatment’s safety profile was largely consistent with earlier studies, although higher serious adverse events were observed at the highest dose. Biogen plans to present detailed data at the Alzheimer’s Association International Conference (AAIC) in London, July 12-15, 2026.

The IONS Link Up

Diranersen was originally discovered by Ionis Pharmaceuticals (IONS), with Biogen acquiring exclusive global rights in December 2019.

The Celia study enrolled 416 patients with early-stage Alzheimer’s disease, including those with mild cognitive impairment and mild dementia. The trial tested three different doses of Diranersen over a 76-week placebo-controlled period.

The stock has gained more than 16% year to date.

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