Mitapivat cleared only one of its two RISE UP Phase 3 primary endpoints — a hemoglobin response rate that met statistical significance against a pain crisis reduction endpoint that did not — yet Agios has moved straight to an accelerated approval filing with the FDA. That is the central tension in this submission, and it shapes everything downstream.
The sNDA rests on the hemoglobin response endpoint: a ≥1.0 g/dL increase from baseline in average hemoglobin concentration from Week 24 through Week 52, achieved in the 2:1 randomized, double-blind RISE UP Phase 3 trial across 207 participants aged 16 and older. Within the subset of responders, Agios reports clinically meaningful reductions in pain crises, hospitalizations, and patient-reported fatigue — but those are subgroup findings, not the top-line result the trial was powered to deliver on vaso-occlusive crises. FDA is being asked to treat a surrogate biomarker improvement, hemoglobin concentration, as reasonably likely to predict clinical benefit in a disease where the pain crisis is the defining patient experience. That is a legitimate accelerated approval argument, but it is a harder sell when the trial itself tested a clinical endpoint directly and came up short.
The confirmatory trial design — 159 patients aged 12 and older, placebo-controlled, 52 weeks, with transfusion freedom from Week 4 through Week 52 as the primary endpoint — is notably narrower and younger than RISE UP Phase 3, which enrolled from age 16. Shifting to transfusion burden rather than pain crisis as the confirmatory outcome suggests Agios and FDA negotiated around the failed endpoint rather than retesting it. Transfusion dependence is a meaningful outcome for a subset of sickle cell patients, but it does not map directly onto the broader population burdened primarily by vaso-occlusive events. The confirmatory trial must be underway at the time of any approval decision, so enrollment pace on that 159-patient study becomes operationally critical to the entire program’s trajectory.
PDUFA timing will clarify FDA’s appetite after the 60-day filing review expected in Q3 2026, but the number to track is the hemoglobin responder rate from the full RISE UP dataset when Agios presents at EHA on June 13 — because the size and consistency of that responder fraction is the foundation on which any accelerated approval label will stand or fall.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
