Mirum Pharmaceuticals (MIRM) traded lower on May 4, 2026, despite announcing that volixibat met the primary endpoint in the VISTAS Phase 2b study in patients with primary sclerosing cholangitis (PSC). The company reported a statistically significant reduction in cholestatic pruritus, including a 2.72-point improvement from baseline and a 1.64-point placebo-adjusted difference on the Adult ItchRO scale (p<0.0001), but the shares slid as investors recalibrated expectations immediately after the catalyst. (stocktitan.net)

Beyond the headline, the market focus is shifting to the “quality” of the readout: timing of response (improvements observed within two weeks), tolerability (gastrointestinal adverse events and liver lab elevations consistent with IBAT inhibition), and discontinuations. Mirum also flagged its regulatory path, with a pre-NDA meeting with the FDA scheduled for summer 2026 and a planned NDA submission in the second half of 2026, which can concentrate attention on remaining execution risk rather than the endpoint itself. (stocktitan.net)

Mirum scheduled an investor conference call for May 4 at 8:30 a.m. ET to discuss the clinical readout, setting up a near-term forum for Q&A on safety, subgroup analyses, and regulatory strategy. The calendar also remains catalyst-heavy, with the company set to report first-quarter 2026 financial results on May 6, 2026, which can shift sentiment if commercial trends or spending guidance surprise relative to expectations. (stocktitan.net)