Abivax reported positive Phase 3 efficacy for obefazimod (miRNA-124 enhancer) in ulcerative colitis maintenance, but the company disclosed malignancy cases among participants that weighed on investor sentiment. The trial, branded Abtect, met primary and key secondary endpoints in both the 25-mg and 50-mg cohorts, while no malignancies other than non-melanoma skin cancer were reported in the 25-mg group. Wall Street’s focus shifted to three cancer cases other than non-melanoma skin cancer reported in the 50-mg cohort: one prostate cancer during induction, one breast cancer, and one case of colonic dysplasia. Abivax’s shares fell sharply following the top-line readout despite the efficacy signal described as among the strongest reported for long-term UC maintenance. The results highlight the ongoing tightrope for immune-modulating epigenetic therapies in chronic inflammatory disease, where durability and safety signals can emerge late in development. For drug developers, it also reinforces the importance of transparent adjudication and malignancy monitoring in maintenance trials. Regulatory and payer implications will likely hinge on how the cases are characterized and what follow-up data Abivax provides beyond the topline readout.