Biogen decided to advance diranersen (BIIB080) into registrational trials for early Alzheimer’s disease despite missing the primary dose-response endpoint in a Phase 2 study. Biogen reported reductions in cerebrospinal fluid tau and tau pathology alongside cognitive slowing, with the lowest dose showing the most favorable signals. Analysts cited continued uncertainty around the dose-response results, while Biogen’s rationale emphasized biomarker and efficacy signals not seen with prior tau-targeting agents. The decision keeps Biogen’s tau franchise in play as companies navigate a difficult history of failed Alzheimer’s endpoints. For developers, the move reinforces how biomarker-driven interpretation can reshape registrational strategies when primary efficacy endpoints do not align cleanly with mechanistic readouts.