Sanofi disclosed setbacks for tolebrutinib, the BTK inhibitor it acquired for about $3.7 billion: a Phase 3 trial in primary progressive multiple sclerosis failed to meet its endpoints, and a separate U.S. approval decision has been delayed. The company said the mixed results affect different MS populations and that regulatory timelines have shifted as a result. BTK inhibitors target B-cell signalling and have been pursued as oral alternatives for various MS subtypes; Sanofi’s announcements prompted reassessments of development paths and near-term commercial expectations.