Actions of Abivax It closed down 43.6% on Tuesday after reporting new data on its top asset, an ulcerative colitis drug, wiping out billions in market capitalization and raising questions about how a potential acquisition of the French biotech could play out.
The drug met its endpoints of demonstrating clinically significant efficacy and a placebo-adjusted remission rate of approximately 40% for both doses tested, but it also showed that there were cases of cancer among patients taking the higher dose.
“[The] “The cancer signal complicates things,” said a Jefferies analyst. “Even if there is unrelated noise, we believe the excess will be real, especially considering the absence of other data events influencing the value over the next few years.” [year]”.
In the study cohort, one case of prostate cancer, breast cancer and colon dysplasia were reported, which Abivax researchers considered unrelated to the treatment, with no specific organ clustering observed.
There were also four cases of skin cancer with the highest dose of 50 mg, of which two were considered unrelated or unlikely to be related to the drug, and the other two had a medical history of skin cancer, Abivax said.
Jefferies analysts said “a reasonable explanation” for the cancer cases was plausible but “doesn't seem like an easily dismissable excess,” and downgraded the stock to Hold from Buy.
The Paris-listed stock gained nearly 1,700% in 2025, but the stock had fallen 7% at the start of trading on Tuesday.
Abivax stock so far this year.
The trial results, published late Monday, come from a maintenance study in which Abivax evaluated the effect of the drug obefazimod over 44 weeks. It comes after results from a late-stage trial in mid-2025 surpassed even the most optimistic expectations.
Analysts have described the experimental drug as the best potential treatment for ulcerative colitis (UC). Abivax is also testing the drug for Crohn's disease, opening it to a multibillion-dollar market for irritable bowel syndrome (IBS).
“The novel mechanism, sustained clinical remission, and favorable long-term safety profile highlight its potential to address an important unmet need in UC.“,” said David Rubin of Abivax, also director of the inflammatory bowel disease center at the University of Chicago Medicine.
“While the signal of malignancy cannot be ignored, we view it as potential overlabeling rather than evidence of a clear causal risk to safety,” said Stifel analyst Damien Choplain, noting that the efficacy data was strong.
AbbVie's Rinqvoc, another drug for ulcerative colitis and other inflammatory conditions, carries a malignancy warning from the U.S. Food and Drug Administration, but still generated $8.3 billion in sales in 2025, he added.
Acquisition target
Abivax has positioned itself as a prime acquisition 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 have a positive reading and noted that the company was in no rush to secure a deal or partnership as conditions would be better later.
Abivax was widely expected to be acquired before launching obefazimod, and de Garidel told CNBC he was planning to raise money after the June data readout. The company on Monday reiterated the expectation to submit obefazimod for FDA approval in the fourth quarter and a possible launch in 2027.
According to Choplain, the most likely scenario now is that Abivax waits for the full data set, expected to be revealed in October, to become more granular and confirm that the malignancies are not related to the treatment.
It also seems reasonable to assume that potential buyers will wait for the full data set before making a decision, he told CNBC by email on Tuesday.
