Sanofi shares seen down 1-2% after it ends Riliprubart Phase 3 study on efficacy concerns - traders

Sanofi shares fell 1-2% in early trading on Monday, June 10, 2026, as traders reacted to news that the company has ended its Phase 3 trials for riliprubart, a C1s complement inhibitor being developed for chronic inflammatory demyelinating polyneuropathy (CIDP), due to concerns over efficacy. The decision marks a significant setback for the drug, which had shown promising results in earlier-stage trials.

Riliprubart had advanced to two global Phase 3 studies—MOBILIZE (NCT06290128) and VITALIZE (NCT06290141)—after demonstrating encouraging efficacy and safety in a Phase 2 trial. In that study, the drug showed improvement or stability in over 80% of participants across three cohorts, including those who had failed or had an inadequate response to standard-of-care (SOC) treatments. However, the decision to halt further development suggests that the drug did not meet the necessary efficacy thresholds in later-stage testing.

The Phase 2 trial had also highlighted riliprubart’s ability to reduce neurofilament light chain (NfL) levels by 35%, a biomarker associated with CIDP progression, and to improve patient-reported outcomes such as fatigue and quality of life. Despite these findings, the termination of Phase 3 trials indicates that the drug may not have demonstrated sufficient clinical benefit to justify continued investment.

Sanofi has not yet issued an official statement confirming the termination of the trials or providing further details on the reasons behind the decision. However, traders and analysts speculate that the move reflects unmet expectations in the latest data review. The company had previously emphasized the unmet need in CIDP treatment and the potential of riliprubart to address this gap.

The stock’s decline underscores the market’s sensitivity to late-stage clinical outcomes and highlights the risks inherent in pharmaceutical R&D. Investors will now be watching closely for any updates from Sanofi and how this development might affect its broader pipeline and financial outlook.