Core Viewpoint - Sanofi's tolebrutinib, an investigational treatment for non-relapsing secondary progressive multiple sclerosis (nrSPMS), has received a complete response letter (CRL) from the FDA, indicating a significant setback in its regulatory approval process [1][3]. Regulatory Update - The FDA's review of tolebrutinib is expected to extend beyond the previously set target action date of December 28, 2025, with further guidance anticipated by the end of Q1 2026 [2]. - Sanofi has submitted an expanded access protocol for tolebrutinib in response to an FDA request [2]. Company Response - Sanofi expressed disappointment regarding the FDA's decision, emphasizing the unmet medical need for addressing disability progression in MS and the importance of considering expert and patient perspectives in the review process [3]. Product Background - Tolebrutinib is a brain-penetrant Bruton's tyrosine kinase inhibitor designed to target neuroinflammation, a key factor in disability progression in MS [6]. - The drug was provisionally approved in the UAE in July 2025 for treating nrSPMS and is under review in the EU and other regions [4]. Financial Considerations - Sanofi is conducting an impairment test on the intangible asset value of tolebrutinib, with results expected to be reported alongside Q4 and FY 2025 results in January 2026. This test will not impact the company's net income or financial guidance for 2025 [5]. Commitment to Innovation - Tolebrutinib reflects Sanofi's dedication to developing innovative treatments for neurological diseases, aiming to transform the treatment landscape for conditions like MS and other neuro-inflammatory disorders [7].