shares of Abibax The company closed 43.6% lower on Tuesday after releasing new data on its flagship asset, a drug to treat ulcerative colitis, wiping out billions of dollars in market capitalization and raising questions about how a potential acquisition of the French biotech company would play out.
Although the drug met its endpoints of clinically meaningful efficacy and a placebo-adjusted remission rate of approximately 40% at both doses tested, it also showed that there were cancer cases among patients who took the higher doses.
“Cancer signs complicate matters,” Jefferies analysts said. “We believe the overhang is real, even if it is extraneous noise, especially considering there are no other data events that will impact value in the coming year (1 year).”
One case each of prostate cancer, breast cancer, and colon dysplasia was reported in the study cohort, but Avivax said these were not observed to be organ-specific clustered and appeared to be unrelated to the researchers’ treatment.
Avivax said there were four cases of skin cancer at the high dose of 50 mg, two of which were considered unrelated or unlikely to be related to the drug, and two who had a history of skin cancer.
Analysts at Jefferies downgraded the stock from “buy” to “hold,” saying that while a “rational explanation” for the cancer cases is plausible, “we do not believe this is an overhang that can be easily ignored.”
The Paris-listed stock rose nearly 1,700% in 2025, but the stock was down 7% as of Tuesday trading.
Avivax stock price from the beginning of the year to the present.
The trial results announced late Monday were from a maintenance study in which Avivax evaluated the effectiveness of the drug obefazimod over 44 weeks. It was announced after late-stage trial results in mid-2025 exceeded even the most optimistic expectations.
Analysts say the experimental drug has the potential to be a best-in-class treatment for ulcerative colitis (UC). Avivax is also testing a treatment for Crohn’s disease, opening the door to a multibillion-dollar market for irritable bowel syndrome (IBS).
“The novel mechanism, sustained clinical remission, and favorable long-term safety profile highlight the potential of addressing an important unmet need in UC,” said Avivax’s David Rubin, director of the Center for Inflammatory Bowel Disease at the University of Chicago Medicine.
Stifel analyst Damien Choplein said the efficacy data were strong, saying, “While the adverse signal cannot be ignored, we view it as a potential labeling overhang rather than evidence of a clear causal safety risk.”
AbbVie Rinqvoc, another treatment for ulcerative colitis and other inflammatory conditions, is expected to generate $8.3 billion in sales in 2025 despite a U.S. Food and Drug Administration warning about malignancy, he added.
Acquisition target
Avivax has been positioned as a prime acquisition target, with unconfirmed rumors that the drug giant is eyeing the clinical-stage biotech led by CEO Marc de Garidel.
De Garridel told CNBC in March that he was confident of a positive outcome from the retention study and suggested he was in no hurry to secure a contract or partnership as terms would improve thereafter.
Avivax is widely expected to be acquired before the launch of obefazimod, and de Garidel told CNBC that the company plans to raise money after the release of the June numbers. The company reiterated Monday that it expects to file for FDA approval for obefazimod in the fourth quarter and potentially launch it in 2027.
The most likely scenario for now, Choplane said, is for Avivax to wait for the full data set, expected to be released in October, to gain more precision and confirm that the malignancy is not related to the treatment.
He told CNBC in an email Tuesday that it seems reasonable to assume potential buyers would wait for the full data set before taking action.
