Abivax Shares Crater 30% After Cancer Cases Surface in Bowel Drug Trial

CNBC reported Tuesday that the Abivax stock drop exceeded 30% after the French biotech published fresh maintenance trial data for its lead ulcerative colitis drug, obefazimod, raising safety questions that overshadowed otherwise positive efficacy results.

Trial Data Shows Promise but Flags Cancer Cases

Shares in Abivax fell as much as 32% in early Tuesday trading. The 44-week maintenance study showed obefazimod hit its primary endpoints. Both doses tested produced a remission rate of roughly 40%, meeting the bar for clinically meaningful efficacy. However, the data also recorded cancer cases among patients assigned to the higher dose. The company stated that investigators considered those cases unrelated to the drug, with no clustering around any specific organ.

Analysts Warn the Overhang Could Linger

Wall Street was not fully reassured. A Jefferies analyst told CNBC that even if the cancer findings ultimately prove to be unrelated noise, the overhang on the stock is likely to persist. The analyst noted there are few other value-creating data readouts expected over the next year. That absence of near-term catalysts makes it harder for Abivax to quickly rebuild investor confidence.

A Remarkable Run Now Under Pressure

Abivax had been one of the most closely watched names in European biotech. The stock surged nearly 1,700% in 2025, fuelled by a mid-year late-stage trial that beat even the most bullish forecasts. Analysts had begun describing obefazimod as a potential best-in-class therapy for ulcerative colitis. The company is also running trials in Crohn’s disease, a move that would open access to a multi-billion-dollar inflammatory bowel disease market. David Rubin, director of the inflammatory bowel disease center at the University of Chicago Medicine and an Abivax collaborator, said the 44-week data demonstrated the drug’s potential for durable disease control and a favorable long-term safety profile.

Takeover Speculation Adds Another Layer

Abivax has attracted persistent acquisition speculation, with large pharmaceutical companies said to be watching the clinical-stage firm closely. CEO Marc de Garidel had previously signaled the company was in no rush to strike a deal, suggesting that upcoming trial data could strengthen its negotiating hand. Tuesday’s safety flag complicates that calculus. A prolonged share price decline could shift leverage away from Abivax in any future partnership or buyout discussions. The stock had already shed 7% before Tuesday’s open, meaning the decline extends a streak that had begun before the new data landed. Shares were last trading down more than 27% as of the CNBC report.

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