Abivax stock falls on cancer cases despite strong ulcerative colitis phase 3 data

Abivax's stock tumbled as the company announced strong efficacy for its ulcerative colitis drug obefazimod in a Phase 3 maintenance trial, but also reported several cancer cases in patients receiving the higher 50 mg dose.

The trial data showed that obefazimod maintained remission at 44 weeks, with the 50 mg regimen yielding a 46.7% remission rate versus 27.3% for placebo, meeting the primary endpoint and a key secondary endpoint.

In the maintenance study, on the 50 mg dose there was one case each of prostate cancer, breast cancer, and colonic dysplasia, and two cases each of basal and squamous cell carcinoma; placebo and 25 mg arms had fewer or isolated lesions.

Analysts and company executives downplayed the cancer risk, noting the small number of cases and the high age and prior-medication exposure of the patient population, but Jefferies has cut its price target and rated the stock a hold, citing a 'real' overhang from the malignancy signal.

Abivax shares fell about 28–32% in premarket or early trading, reversing much of the multi‑hundred‑percent gain the stock had enjoyed since the July 2025 induction‑trial results.