Sanofi disclosed that its BTK inhibitor tolebrutinib failed Phase‑3 trials in multiple sclerosis after missing endpoints in two different disease forms, prompting the company to reassess regulatory timing. The company said clinical data did not meet expectations and that a planned PDUFA timeline will be delayed as programs are re‑evaluated. Sanofi had marketed the asset as a potential blockbuster for MS; the Phase‑3 setbacks force strategic decisions around further development and potential biomarker substudies. The result also highlights competition and execution risk in the crowded BTK and neuroimmunology space.