Abivax SA (EPA:ABVX; NASDAQ:ABVX) saw its shares surge on Euronext Paris Tuesday, jumping 35.77% to €113.10, making it the top performer in the SBF 120 index. The sharp rally followed the release of updated safety and efficacy data late Monday that provided investors with a clearer assessment of cancer risk associated with the company's lead drug candidate, obefazimod, for ulcerative colitis.
The market's focus shifted from raw remission rates to the denominator of patient-years of exposure. Abivax's expanded dataset now encompasses 1,704 patient-years of active drug exposure. In this larger pool, malignancies excluding non-melanoma skin cancer occurred at a rate of 0.35 events per 100 patient-years across all active doses combined. This figure falls within the company's expected background range of 0.30 to 0.70 for ulcerative colitis patients, reassuring investors who had been concerned after a June 1 data release highlighted cancer cases in the higher-dose arm.
However, a closer look at the data reveals a nuance that some investors might overlook. While the all-active malignancy rate supports Abivax's safety case, the 50 mg Phase 3 maintenance dose showed a rate of 0.91 per 100 patient-years, above the upper end of the background band. Yet, the broader integrated rate for the 50 mg dose, combining Phase 2 and Phase 3 data, sits at 0.64, within the expected range. This split underscores the importance of ongoing monitoring as the drug progresses.
Chief Executive Marc de Garidel emphasized that the Part 2 results were substantially expanding the long-term safety database. Dr. Remo Panaccione, director of the IBD Clinic at the University of Calgary, noted that the observed rates were consistent with expected background rates for ulcerative colitis patients, providing further validation.
The new efficacy data also bolstered the bullish case. Among induction non-responders who remained on 50 mg obefazimod, 37.2% achieved clinical remission and 34.5% achieved endoscopic remission at Week 44. For patients who relapsed on the 25 mg dose in Part 1 and switched to 50 mg in Part 2, 45.5% regained clinical remission. These results highlight the drug's potential even in patients who initially did not respond to lower doses.
Broker reaction remained positive. Stifel maintained a buy rating with a €115 price target, while Oddo BHF kept an outperform rating and €120 target. Oddo noted that while the new analyses do not definitively prove absence of risk, they offer much greater reassurance than the initial maintenance readout. The stock's year-to-date loss was trimmed to 6.06%, and U.S.-listed shares had jumped 26.4% in extended trading.
Competition in the ulcerative colitis space remains intense. Merck & Co. (NYSE:MRK) recently reported that its tulisokibart met main and key secondary goals in a late-stage trial, though analysts noted the lack of numerical detail limited direct read-through for rivals. Abivax is pressing ahead with its regulatory timeline, targeting a fourth-quarter 2026 U.S. FDA filing for obefazimod in ulcerative colitis.
Looking ahead, Abivax has several key milestones on the calendar. The company is scheduled to report first-half 2026 results on September 21, followed by the NDA filing in the fourth quarter. Mid-2027 topline data from a Phase 2b Crohn's disease induction trial are also expected, which could further expand the drug's potential market.
