Biogen Moves Alzheimer's Drug Diranersen to Phase 3 After It Failed Its Primary Goal in Mid-Stage Trial
Biogen is advancing its tau-targeting drug diranersen to late-stage trials even though it missed the main goal of its Phase 2 study. The company is hanging its hat on secondary signals — biomarker improvements and slower cognitive decline at the lowest dose. Whether that's bold scientific judgment or corporate spin is the question every investor and patient should be asking.
The Drug Failed Its Main Test. Biogen Is Moving Forward Anyway. Biogen announced Thursday that it will advance diranersen — also known as BIIB080 — into Phase 3 registrational trials. The problem: the drug just failed its primary endpoint in Phase 2. The Phase 2 CELIA study enrolled more than 400 patients with mild cognitive impairment or mild Alzheimer's disease. According to BioSpace, the trial's primary goal was a dose-response change in disease severity at 76 weeks, measured by a clinical dementia scale. Diranersen did not meet that goal. Not at the high dose. Not at the middle dose. Not at any dose. So why is Biogen moving forward? What Biogen Says It Found The company isn't throwing in the towel on diranersen — it's pivoting to secondary signals. Biogen's Head of Development Dr. Priya Singhal told CNBC the results are "compelling," citing what she called an "unprecedented combination of tau reduction in pathology and the cognitive benefit." Specifically, Biogen is pointing to two things. First, a "robust biomarker impact" — diranersen reduced tau concentrations in the cerebrospinal fluid, according to BioSpace. Second, a pre-specified analysis of cognitive endpoints showed slower clinical decline across all doses tested. The effect was strongest at the lowest dose — 60 mg every 24 weeks. That last part is scientifically unusual. Drugs typically show stronger effects at higher doses. The fact that the lowest dose outperformed the higher ones is either a meaningful biological signal or a statistical quirk. We don't know which yet, because Biogen has not released the actual data. The Data Blackout Is a Problem Biogen disclosed ZERO numbers in its press release. According to BioSpace, the company "did not provide data in its news release," sharing only qualitative descriptions of the results. No percentages. No p-values. No effect sizes. Nothing. Detailed data from CELIA won't be presented until the Alzheimer's Association International Conference in July. That's two months away. Biogen is asking the market — and ultimately patients — to trust its interpretation of results nobody else has seen yet. Analysts flagged this immediately. Stifel wrote Thursday, "We want to be a little cautious here until we see the full data. Candidly we don't know" — the quote cuts off there, but the skepticism is real. RBC Capital Markets acknowledged the drug "could be a big long-term win" while noting Biogen's "excitement" only "suggests there may be something here." BMO Capital Markets called the cognitive findings "a broad positive for Alzheimer's development" but stopped short of declaring victory. Biogen's stock ticked up about 4% in pre-market trading after the announcement, according to BioSpace. The market is cautiously intrigued. Biogen's Track Record Demands Scrutiny This company has been down this road before. Multiple times. Biogen spent years and billions developing Aduhelm, an amyloid-targeting Alzheimer's drug. The FDA approved it in 2021 over the objections of its own advisory committee — a controversial decision that CNBC reported led to massive backlash. Medicare refused to broadly cover it. Biogen eventually pulled the drug from the market. A commercial and scientific disaster. Biogen then partnered with Eisai on lecanemab, marketed as Leqembi. The New York Times reported in 2022 that lecanemab reduced cognitive decline by 27% compared to placebo in a nearly 1,800-patient trial — a genuinely significant result that earned FDA approval. That drug is on the market. So Biogen's Alzheimer's record is: one failure, one success, and now one drug advancing on ambiguous data. This demands a high standard of transparency from the company. The Tau Angle Is Legitimate Science Fair point in Biogen's favor: diranersen targets tau, NOT amyloid. That's a different mechanism entirely. For decades, the Alzheimer's field poured resources into clearing amyloid plaques from the brain. Results were mixed. Tau — a protein that forms tangles inside neurons and is closely correlated with cognitive decline — has emerged as an alternative target. Eli Lilly is also developing tau-targeting drugs, according to CNBC, which signals serious scientific interest across the industry. An antisense oligonucleotide like diranersen works by limiting tau production at the genetic level. If it actually reduces tau in cerebrospinal fluid AND slows cognitive decline, that's a meaningful finding — even if the clinical dementia scale didn't budge the way the trial was designed to show. The mechanism is sound. The secondary signals are worth investigating. Phase 3 is not an unreasonable decision. Releasing the actual numbers would cost Biogen nothing and would tell us whether this is real. What This Means for Patients and Taxpayers About 7 million Americans are living with Alzheimer's disease. There is no cure. Existing treatments slow decline modestly — they do
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