Abivax’s Ulcerative Colitis Drug Shows High Remission Rates Amid Cancer Safety Concerns

Abivax’s Phase 3 ABTECT maintenance trial evaluated obefazimod in a 44-week, double-blind study of patients with moderately to severely active ulcerative colitis. The 25 mg and 50 mg once-daily doses achieved clinical remission in 50.8 % and 51.3 % of participants, respectively, versus 10.4 % on placebo. Placebo-adjusted remission differences were 39.3 and 40.3 percentage points, meeting the FDA’s primary endpoint.

Abivax stock crashes as safety fears overshadow bowel disease drug trial winBioPharmaDiveReutersCNBCBloombergCNBC

Abivax’s stock rose more than 16-fold in 2025, gaining roughly 1,700 % before the June 2 announcement. The company, led by CEO Marc de Garidel, has been cited as a prime acquisition target, with rumored suitors including Eli Lilly, AstraZeneca, Takeda and Pfizer. The drug’s oral, once-daily format and a novel mechanism that up-regulates miR-124 have been highlighted as differentiators.

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In addition to the remission rates, the trial met all key secondary endpoints, including endoscopic improvement and corticosteroid-free remission. Safety data identified three malignancies in the 50 mg arm—one each of prostate cancer, breast cancer and colonic dysplasia—and four skin-cancer cases (two with prior history, two deemed unlikely related). Investigators classified all cancer events as unrelated to treatment, and a single cancer case also occurred in the placebo group.

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Shares fell 30 % in early Paris trading, later sliding as much as 43.6 % by day-end, erasing several billion euros of market value. Analysts downgraded the stock from “Buy” to “Hold,” citing the cancer signal as a new overhang amid an otherwise strong efficacy profile.

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Abivax’s release emphasized that the independent monitoring committee found no causal link between obefazimod and the malignancies and that the overall safety profile remained favorable. The company confirmed plans to submit a New Drug Application to the U.S. FDA in late 2026 and noted ongoing trials of obefazimod in Crohn’s disease, with results expected next year.

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Jefferies analysts warned that “the cancer signal complicates matters” and that even if unrelated, the overhang could affect investor sentiment, strategic options and commercial uptake. Stifel’s Damien Choplain described the signal as a “potential labelling overhang rather than evidence of a clear causal safety risk.” Truist highlighted that unresolved safety questions could drive further share volatility.

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While Jefferies and Stifel stress a lingering risk, Van Lanschot Kempen analysts argued the signal appears “more as noise than a true malignancy risk.” Yale Jen of Laidlaw & Company called the overall results a “homerun” for the drug’s development, underscoring divergent market interpretations.

Bloomberg

Abivax aims to file its U.S. NDA by the fourth quarter of 2026. Pending regulatory clearance, the drug could target peak annual sales of $5 billion per indication, expanding the $20 billion inflammatory bowel disease market toward $30 billion by decade’s end. The pending Crohn’s disease data and ongoing acquisition interest will shape the company’s strategic trajectory.

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• “[The] cancer signal complicates matters,” — Jefferies analyst

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• “Even if unrelated noise, we think the overhang will be real, especially considering absence of other value-inflecting data events over the next [year].” — Jefferies analyst

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• “While the malignancy signal cannot be ignored, we view it as a potential labelling overhang rather than evidence of a clear causal safety risk,” — Stifel analyst Damien Choplain

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• “We see the signal more as noise than a true malignancy risk,” — Van Lanschot Kempen analyst Sebastiaan van der Schoot

Bloomberg

• “The novel mechanism, sustained clinical remission, and favorable long-term safety profile highlight its potential to address a significant unmet need in UC,” — David Rubin, Director, Inflammatory Bowel Disease Center, University of Chicago Medicine

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