Abivax (ABVX) saw its stock collapse by 44% on Tuesday, closing at €63.10 on Euronext Paris, despite reporting positive late-stage trial results for its lead drug candidate, obefazimod. The sharp decline came as investors focused on safety signals, including cancer and dysplasia cases observed in the higher-dose arm of the study.
The stock opened at €111.80 on Monday but dropped to as low as €62.80 during the session. In the U.S., the company's Nasdaq-listed American Depositary Receipts fell roughly 44% to $72.86. The selloff erased a significant portion of the gains that had made Abivax one of Europe's most prominent biotech bets, with shares having surged more than 16-fold over the past year.
Abivax reported late Monday that both the 25 mg and 50 mg once-daily doses of obefazimod met the primary endpoint of clinical remission in a Phase 3 maintenance trial for ulcerative colitis. Remission rates were 50.8% for the 25 mg group and 51.3% for the 50 mg group, compared to 10.4% for placebo. The placebo-adjusted differences were 39.3 and 40.3 percentage points, respectively. All key secondary endpoints, including endoscopic improvement and corticosteroid-free remission, were also achieved.
However, the safety data overshadowed the efficacy results. In the 50 mg arm, there was one case each of prostate cancer, breast cancer, and colonic dysplasia—an abnormal cell growth that can precede cancer. Investigators determined the cases were unrelated to the drug, and the company noted no organ-specific clustering. Despite these reassurances, the market reacted negatively, viewing the imbalance as a potential regulatory hurdle.
CEO Marc de Garidel called the data "compelling," citing "durable efficacy and favorable safety profile." Dr. David T. Rubin of the University of Chicago Medicine added that the 44-week data showed "meaningful efficacy and durable disease control." Analysts were divided. Jefferies termed the cancer cases a "blow to their thesis," warning of negative sentiment even without a clear drug link. Truist Securities noted that uncertainty over causality could lead to continued share volatility. Laidlaw & Company's Yale Jen described the selloff as an "overreaction" and called the readout a "homerun." Leerink Partners' Thomas Smith said the results "clearly exceeded expectations," while Stifel's Damien Choplain acknowledged the malignancies as an "introduced uncertainty that cannot be ignored."
The competitive landscape adds pressure. Abivax is positioning obefazimod as a once-daily oral therapy, but it faces entrenched rivals like AbbVie's Rinvoq, which carries an FDA boxed warning for malignancy risk, and Takeda's Entyvio. The presence of malignancy cases in the high-dose arm could lead to more restrictive labeling or heightened regulatory scrutiny, potentially limiting physician adoption even if the drug gains approval.
Abivax plans to file a New Drug Application with the FDA in the fourth quarter of 2026. The company expects to report half-year financials on September 21 and anticipates top-line Phase 2b induction data for Crohn's disease around mid-2027. For now, the stock is trading as a regulatory-risk play, with the market discounting the strong efficacy data and focusing instead on the safety concerns that could shape the drug's commercial future.