Zenas Biopharma reported positive Phase III Indigo results for obexelimab in immunoglobulin G4‑related disease (IgG4‑RD), meeting the primary endpoint with a 56% reduction in flare risk versus placebo over 52 weeks. Despite statistically significant efficacy, Zenas shares plunged after investors compared the effect size unfavorably to Amgen’s Uplizna, which produced a larger risk reduction in its pivotal study. Company management said obexelimab’s non‑depletion mechanism and tolerability could position the drug as a maintenance option, particularly for older patients. Zenas plans a BLA submission in the U.S. in the second quarter. The market reaction highlights how cross‑trial comparisons and existing label incumbents can overshadow absolute positive readouts for rare-disease assets. Regulators will evaluate the full dataset; commercial prospects will hinge on label differentiation, safety profile, and physician adoption versus B‑cell‑depleting alternatives.