Sanofi presented data from a failed Phase 3 trial of the BTK inhibitor tolebrutinib in primary progressive multiple sclerosis (PPMS), explaining the company’s decision to withdraw from that indication. The data—discussed at ACTRIMS26—prompted investigators to examine trial design, patient selection, and biological rationale for the negative outcome. Sanofi’s disclosure underscores how late‑stage failures can prompt program pivots and reallocation of R&D capital. Competing BTK programs and the broader MS drug pipeline will be evaluated in light of these findings as companies reassess biomarkers, endpoints, and subgroup signals that might salvage or redirect development efforts.