Biogen advanced diranersen (BIIB-080) into registrational trials for early Alzheimer’s disease despite missing a key phase II primary endpoint, signaling that tau-pathology and biomarker effects may be outweighing efficacy metrics in late development planning. In the Celia trial, Biogen reported dose-dependent slowing of clinical decline and reductions in cerebrospinal fluid tau, even as the study missed on its primary dose-response measure on the Clinical Dementia Rating-Sum of Boxes. Analyst reactions in the report were mixed: some emphasized uncertainty around the dataset and the risk of choosing the wrong regulatory path, while others argued that the trial still represented an important scientific advance for tau-targeting therapies. The biotech takeaway is clear: the direction of Alzheimer’s drug development remains highly sensitive to biomarker interpretation and endpoint design, and sponsors are willing to move forward when tau targeting generates credible downstream signals.