Biogen reported that diranersen (BIIB080), a tau-targeting Alzheimer’s therapy, missed its primary dose-response efficacy endpoint in a Phase 2 study. The company said lower tau levels in spinal fluid and brain correlated with slower cognitive decline, with the lowest dose showing the strongest signal—though the overall primary goal was not met. The mid-stage outcome adds another data point for tau-directed programs seeking clinical efficacy while navigating endpoint design and dose selection. Biogen’s next steps could hinge on how the company frames the biomarker–cognition relationship and whether it sees a path toward confirmatory studies. The results also intensify competitive pressure in the Alzheimer’s pipeline, where successive failures and mixed readouts continue to define near-term capital allocation and partnership decisions.