Shares of French biotech Abivax tumbled as much 32% after it reported fresh data on its lead asset, a drug for ulcerative colitis.
The medicine met its endpoints of demonstrating a clinically meaningful efficacy and a remission rate of about 40% for both doses tested, but also showed that there were cancer cases among patients taking the higher dose.
“[The] cancer signal complicates matters,” a Jefferies analyst said. “Even if unrelated noise, we think the overhang will be real, especially considering absence of other value-inflecting data events over the next [year].”
In the study cohort, there was one reported case each of prostate cancer, breast cancer, and colonic dysplasia, which Abivax said were unrelated to treatment.
There were also four cases of skin cancer on the higher 50 mg dose, of which two were deemed not or unlikely related to the drug, and the other two had a medical history of skin cancer, Abivax said.
The Jefferies analysts said that “a reasonable explanation” for the cancer cases was plausible, but “doesn’t seem like an easily dismissed overhang.”
The stock gained nearly 1,700% in 2025, but shares had fallen 7% coming into Tuesday trading. It was last trading down over 32%.
Abivax shares year-to-date.
The trial results, published late Monday, were from a maintenance study in which Abivax assessed the effect of the drug, obefazimod, over 44 weeks. It comes after the results of a late-stage trial for an ulcerative colitis medicine in mid-2025, beating even the most optimistic expectations.
Analysts have described the experimental drug as a potential best-in-class treatment for ulcerative colitis. Abivax is also testing the medicine for Crohn’s disease, opening it up to a multi-billion-dollar market for Irritable Bowel Syndrome (IBS).
“The 44-week maintenance data demonstrate obefazimod’s potential to deliver meaningful efficacy and durable disease control in ulcerative colitis,” said Abivax’s David Rubin, also director of the inflammatory bowel disease center at the University of Chicago Medicine.
“The novel mechanism, sustained clinical remission, and favorable long-term safety profile highlight its potential to address a significant unmet need in UC.”
The company has been positioned as a prime takeover target, with unconfirmed rumors that big pharma has its eyes on the clinical-stage biotech led by CEO Marc de Garidel.
De Garidel told CNBC in March that he was confident the maintenance study would read out positively, and signaled that the company was in no rush to secure a deal or a partnership, as terms would be better after it.
It has been widely expected that Abivax would be acquired before launching obefazimod, and de Garidel told CNBC that it was planning to raise money after the June data readout.
