Sanofi announced that the U.S. Food and Drug Administration has postponed its review of the company’s brain‑penetrant Bruton’s tyrosine kinase inhibitor, tolebrutinib, until the end of the first quarter of 2026. The delay follows the agency’s request for additional data and a revised clinical development plan for the drug’s indication in non‑relapsing secondary progressive multiple sclerosis (nrSPMS). At the same time, Sanofi disclosed that the Phase III PERSEUS trial for primary progressive multiple sclerosis (PPMS) failed to meet its primary endpoint, leading the company to abandon plans for regulatory registration in that indication.
Tolebrutinib was acquired by Sanofi in 2020 as part of its $3.7 billion purchase of Principia Biopharma. The oral, brain‑penetrant BTK inhibitor is designed to target smoldering neuroinflammation that drives disability progression in MS. The drug previously received breakthrough therapy designation in December 2024 and was provisionally approved in the United Arab Emirates in July 2025 for nrSPMS. Despite these milestones, the PERSEUS trial’s negative result and the FDA’s request for more data underscore the challenges Sanofi faces in bringing a new MS therapy to market.
Sanofi’s broader financial performance provides context for the impact of these setbacks. In Q4 2024, the company reported sales of €10.564 billion and a business earnings‑per‑share of €7.12, while full‑year 2024 revenue reached €41.081 billion. Q3 2025 sales rose to €12.43 billion, but the company’s business EPS fell to €2.91, reflecting the heavy R&D investment in its MS pipeline. The tolebrutinib delays and trial failure add uncertainty to the projected €1.4 billion in peak sales that the drug was expected to generate, and Sanofi has stated that the impairment charge evaluation for tolebrutinib’s intangible value will not affect net income or earnings per share.
The market reacted sharply to the dual setbacks. Sanofi’s shares fell roughly 6 % at the open on December 15, 2025, the steepest decline since early September. Analysts cited the FDA’s postponement of the nrSPMS review and the PERSEUS trial failure as the primary drivers of the sell‑off, noting that the combined events cast doubt on the drug’s future approval and peak sales potential. The reaction reflects investors’ concerns about Sanofi’s ability to diversify growth beyond its blockbuster Dupixent and the competitive pressure in the MS market.
Management acknowledged the disappointment and outlined a strategic response. Houman Ashrafian, Sanofi’s Executive Vice President of Research & Development, said the company is disappointed by the PERSEUS results but remains committed to advancing the remaining MS indications. He added that the additional time granted by the FDA will allow Sanofi to collect a more robust data set, but the company will also reassess resource allocation toward other assets in its pipeline. Ashrafian emphasized that Sanofi’s transformation into a focused, science‑driven biopharma company will guide future investment decisions, balancing the need for new therapies with the imperative to protect shareholder value.
The dual setbacks highlight the risks inherent in late‑stage drug development and the importance of regulatory alignment. While the FDA’s request for more data may ultimately lead to a stronger submission, the failure in PPMS and the delay in nrSPMS introduce significant headwinds that could delay Sanofi’s entry into a high‑growth market segment. The company’s recent financial strength and ongoing focus on cost discipline provide a buffer, but the event underscores the need for Sanofi to maintain a diversified pipeline and to manage the trade‑off between aggressive R&D investment and realistic revenue expectations.
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