Abivax has proclaimed that its maintenance trial in ulcerative colitis delivered 'landmark' results, and the drug's safety profile has previously been one of its main potential selling points. But Wall Street was rattled by malignancy events that call this into question.

Abivax said its experimental treatment for ulcerative colitis showed significant efficacy in a closely watched trial, but shares of the company tanked on safety concerns.

A handful of cancer cases reported among treatment recipients overshadowed efficacy results analysts described as “best-in-disease” and sent shares down more than 30%.