Abivax shareholders lost more than 40% of their investment value on June 2, 2026, as the stock plunged from a pre-announcement close of approximately $129.69 to as low as $71 per share midday after rare malignancy cases surfaced in the company's Phase 3 ABTECT ulcerative colitis trial for obefazimod. The market reaction was swift and severe. Trading volume surged to more than eight times the daily average on June 2. Jefferies downgraded ABVX from Buy to Hold and cut its price target from $160 to $90 -- a 43.75% reduction -- citing the cancer signal as a material overhang on the stock's outlook. Short interest climbed to approximately 12% of the float within 24 hours of the disclosure. Notably, the stock had initially rallied approximately 20% in after-hours trading on June 1 when the Phase 3 efficacy data were first released. Within hours, as the rare malignancy cases in the treatment arm received broader coverage, the rally reversed entirely and shares collapsed through the prior close. By the midday trading on June 2, ABVX had fallen more than 45%, erasing all gains since mid-August, 2025.