Shares of Abivax The company closed down 43.6% on Tuesday after reporting new data on its lead asset, an ulcerative colitis drug, wiping out billions in market capitalization and raising questions about how a potential takeover of the French biotechnology company might play out.

The drug met its endpoints of clinically meaningful efficacy and a placebo-adjusted remission rate of about 40% for both doses tested, but also showed that there were cases of cancer in patients taking the higher dose.

“[The] “The cancer signal complicates things,” said a Jefferies analyst. “Even if it is unrelated noise, we expect the overhang to be real, especially given the lack of other value-impacting data events in the next few years.” [year].”

One case each of prostate cancer, breast cancer and colon dysplasia were reported in the study cohort, which Abivax said researchers considered unrelated to treatment and no organ-specific clustering was observed.

There were also four cases of skin cancer at the higher 50 mg dose, two of which were 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 that “a reasonable explanation” for the cancer cases is plausible but “does not appear to be an easily dismissed overhang,” and downgraded the stock to “hold” from “buy.”

The Paris-listed stock gained nearly 1,700% in 2025, but shares were down 7% at the start of trading on Tuesday.

Stock chart iconStock chart icon

Abivax shares since the beginning of the year.

The study results released late Monday come from a maintenance study in which Abivax examined the effects of the drug obefazimod over 44 weeks. This came after the results of a late-stage trial in mid-2025 exceeded even the most optimistic expectations.

Analysts have described the experimental drug as potentially the best treatment for ulcerative colitis (UC). Abivax is also testing the drug against Crohn’s disease, opening up a multibillion-dollar market for irritable bowel syndrome (IBS).

“The novel mechanism, sustained clinical remission and favorable long-term safety profile highlight the potential to address a significant unmet need in UC,” said David Rubin of Abivax, also director of the Inflammatory Bowel Disease Center at the University of Chicago Medicine.

“Although the malignancy signal cannot be ignored, we see this as potential labeling overload rather than evidence of a clear causal safety risk,” said Damien Choplain, an analyst at Stifel, noting that the efficacy data were compelling.

AbbVie’s Rinqvoc, another drug for ulcerative colitis and other inflammatory diseases, carries a U.S. Food and Drug Administration malignancy warning but still generated $8.3 billion in sales in 2025, he added.

Takeover target

Abivax has been positioned as a prime acquisition target amid unconfirmed rumors that major pharmaceutical companies are eyeing the clinical-stage biotechnology company led by CEO Marc de Garidel.

Abivax is in no rush to make a deal and is confident that key June trial dates can secure better terms for partnerships, its CEO tells CNBC

De Garidel told CNBC in March he was confident the servicing study would be positive and signaled the company was in no rush to close a deal or partnership because conditions would improve afterward.

Abivax was widely expected to be acquired ahead of Obefazimod’s launch, and de Garidel told CNBC that the company planned to raise money after the data is released in June. The company reiterated Monday that it expects to file for FDA approval for obefazimod in the fourth quarter and a possible launch in 2027.

According to Choplain, the most likely scenario now is that Abivax is waiting for the full data set, expected to be released in October, to provide a more detailed view 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 move, he told CNBC via email on Tuesday.

Choose CNBC as your preferred source on Google and never miss a moment from the most trusted name in business news.