Abivax Shares Jump on Expanded Safety Data for Ulcerative Colitis Drug

Abivax shares rose sharply after the French biotech said expanded safety data for its experimental ulcerative colitis drug showed cancer rates in a larger patient population remained within the range typically seen in the disease.

WSJ reported that Abivax's U.S.-listed shares climbed more than 25% in after-hours trading on June 29 after the update. The move came after a turbulent earlier month for the stock, when investors focused on cancer cases disclosed in the same drug program.

Why investors reacted

The latest reading mattered because the earlier phase 3 trial had left the market with a split verdict. The study met its efficacy goals, but the disclosure of multiple cancer cases triggered a sharp selloff and raised questions about whether the signal could be linked to treatment.

Abivax said the expanded dataset did not show cancer rates outside what is typically seen in ulcerative colitis patients. That did not erase all uncertainty, but it gave investors a larger set of numbers to weigh against the earlier concern.

The company is also trying to move the drug, obefazimod, toward a regulatory filing later in 2026.

The earlier setback

The June 2 phase 3 reporting established the tension around the asset. On one hand, obefazimod hit its trial objectives in ulcerative colitis. On the other, the cancer disclosures overshadowed the efficacy win and sent the shares lower.

At the time, investigators and the company said the cancers were not believed to be treatment-related. Even so, the episode left a major question hanging over the stock: whether the safety profile would hold up with more patients and more follow-up.

The June 29 update was aimed directly at that question. By widening the patient set, Abivax was trying to show the earlier cases were not pointing to a broader safety pattern.

More than a safety repair

The announcement also included efficacy information that helped support the rebound. Abivax said nearly 40% of patients who did not initially respond later entered remission after continuing treatment.

The company also said about 45% of patients who relapsed regained remission after increasing the dose. Those findings matter because they suggest the drug may still help patients even after an initial setback.

For investors, that made the readout more than a safety reassurance. It also added another layer of support for the drug's commercial case if regulators eventually approve it.

What comes next

Abivax has said it plans to seek regulatory approval later this year. That makes the broader safety dataset especially important, because long-term tolerability will shape both regulator scrutiny and physician confidence.

The market will now look for the company's formal filing plans, any fuller presentation of the expanded data, and more analysis on whether the cancer signal has truly been defused.

Abivax is a French biotech focused on inflammatory bowel disease, and obefazimod is its lead experimental ulcerative colitis drug. The stock move suggests investors are willing to revalue the program on the new information, but the question of durability remains open.

For now, the story has shifted from a trial that met efficacy goals but scared investors to one in which a larger safety readout and additional remission data gave the market enough reassurance to bid the shares back up.