Abivax (ABVX) Stock: The Drug Beat Every Benchmark — So Why Is It Down 32%?

TLDR

• Abivax stock fell more than 32% on Tuesday after Phase 3 trial data for its ulcerative colitis drug obefazimod showed strong efficacy but flagged rare malignancy events.
• Clinical remission rates of around 51% at both doses far outpaced the placebo rate of 10.4% and beat analyst expectations.
• Investigators detected malignancies of the prostate, breast, and skin in a small number of patients on the higher dose, though the company says these were unrelated to treatment.
• Jefferies downgraded the stock to Hold, citing the malignancy overhang and a lack of other value-creating data events in the coming year.
• Stifel analysts described the safety signal as a “potential labelling overhang” rather than a clear causal risk, and said approval remains likely.

Abivax stock tumbled more than 32% on Tuesday after the company posted what analysts called “best-in-disease” Phase 3 results for its oral ulcerative colitis drug — only to have the headline numbers overshadowed by a handful of rare cancer cases in trial participants.

Abivax S.A., ABVX

The Paris-listed stock was down over 32% in European trading by mid-morning, wiping out billions in market value for a company that had been trading near $130 just the day before — up from under $10 a year ago.

The drug at the center of the story is obefazimod, a once-daily pill that works by boosting expression of miR-124, an immune response regulator. The idea is to dampen IBD-related inflammation without broadly suppressing the immune system.

In a 44-week Phase 3 study, about 50.8% of patients on the 25mg dose and 51.3% on the 50mg dose achieved clinical remission. The placebo rate was 10.4%.

Those numbers comfortably beat expectations and, according to Stifel analyst Damien Choplain, outperform currently available injectable therapies, which typically show placebo-adjusted remission rates of 19% to 32%.

Malignancy Signal Spooks Investors

The trouble came from a small number of malignancies — prostate, breast, and skin — detected in patients on the higher dose. Abivax said the events were deemed unrelated to treatment and weren’t clustered around a specific organ.

Stifel’s Choplain acknowledged the signal “cannot be ignored” but framed it as a labelling issue rather than proof of cause. He pointed to AbbVie’s Rinvoq — an oral IBD therapy that carries a boxed malignancy warning — which still generated $8.3 billion in revenue last year.

Leerink Partners analyst Thomas Smith noted that widely used IBD drugs Stelara and Entyvio already carry language on their labels about theoretical malignancy risk, and that similar labeling for obefazimod would not make it “commercially uncompetitive” given its efficacy profile.

Approval Timeline Stays On Track — For Now

Abivax said it plans to file for regulatory approval in Q4 2025. The company maintains the malignancy events do not represent a causal safety risk.

Whether regulators agree with that framing — and how the FDA treats the malignancy signal in its review — will be the next key question for investors.

As of Tuesday, the stock had erased most of its past twelve months of gains in a single session.

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