Sanofi disclosed that its BTK inhibitor tolebrutinib failed a Phase III Perseus study in primary progressive multiple sclerosis (PPMS) and warned that the U.S. regulatory review in non‑relapsing secondary progressive MS (nrSPMS) will likely slip past the targeted PDUFA date. The program had been a marquee asset from Sanofi’s prior acquisition strategy. Sanofi said it remains engaged with regulators and submitted an expanded‑access protocol while continuing data analyses. The Phase III miss raises questions about BTK class performance across progressive MS subtypes and will force Sanofi to reassess the development timeline and commercial projections for tolebrutinib. The broader impact touches investor expectations and portfolio planning for neuroinflammation programs; competitors and partners will watch for Sanofi’s next steps, including any post‑hoc analyses or additional trials to define subgroups or biomarkers that might predict benefit.