Abivax stock crashes as safety fears overshadow bowel disease drug trial win

Abivax shares fell 31% even after the French biotech reported strong late-stage data for obefazimod, its experimental treatment for ulcerative colitis.

The once-daily oral therapy met the main goal and all key secondary endpoints in a Phase 3 maintenance study, strengthening the case for a potential new option in a market still led by injectable biologics and other advanced treatments.

But the stock reaction showed that investors were not looking at efficacy alone.

They also focused on cancer cases reported in the higher-dose group, even though trial investigators judged them unrelated to the drug.

Abivax stock: Trial win puts obefazimod in focus

The key result came from Abivax’s Phase 3 ABTECT maintenance trial, which tested 25 mg and 50 mg once-daily doses of obefazimod in patients with moderately to severely active ulcerative colitis.

These were patients who had already responded after the induction phase of treatment.

The maintenance study then asked a more important long-term question: could the drug keep patients well over time?

At week 44, clinical remission rates reached 50.8% in the 25 mg group and 51.3% in the 50 mg group.

That compared with a placebo remission rate of 10.4%. On a placebo-adjusted basis, Abivax reported remission differences of 39.3 percentage points for the lower dose and 40.3 percentage points for the higher dose.

Both doses met the US FDA primary endpoint for clinical remission.

Abivax also said the trial met all key secondary endpoints, including endoscopic improvement, endoscopic remission, corticosteroid-free clinical remission and sustained clinical remission.

For investors, this matters because ulcerative colitis is a chronic disease. Short-term symptom relief can lift a stock for a day.

Durable remission over 44 weeks can change how analysts model a drug’s commercial potential.

Analysts see a best-case readout

The strength of the data drew a bullish response from Leerink Partners analyst Thomas Smith, who described the outcome as a “best-case” scenario for Abivax.

Smith said the drug had shown the best placebo-adjusted clinical remission rates reported in a large Phase 3 ulcerative colitis study.

He also pointed to the low placebo remission rate, saying it “underscores the robustness of the treatment effect” in this type of maintenance trial.

That point is important as in clinical trials, a high placebo response can make it harder to show a drug’s true effect.

Here, the gap between obefazimod and placebo was wide, giving bulls a clearer argument that the drug is doing meaningful work.

Smith also cited the “breadth and consistency” of benefits across endpoints as clinically meaningful, especially because the effect lasted through 44 weeks of maintenance treatment.

He rates Abivax "Outperform".

Other analysts' views have also helped support the broader investment case.

Citizens has carried a Market Outperform rating, while Guggenheim has maintained a Buy rating with a $175 target.

That does not remove risk, but it shows why investors had treated this readout as one of the most important biotech catalysts of the year.