Pfizer Inc. (NYSE:PFE) disclosed the death of a participant in a long-term open-label extension study of marstacimab in patients with hemophilia A or B.

In October 2024, the FDA approved Pfizer’s Hympavzi (marstacimab-hncq) for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adults and pediatric patients with hemophilia A (congenital factor VIII deficiency) or hemophilia B (congenital factor IX deficiency).

European Hemophilia Consortium (EHC), a non-profit, non-governmental organization, reported the update.

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Details Of The Fatal Adverse Event

The patient died on December 14, 2025, after serious adverse events, including a cerebellar infarction followed by cerebral hemorrhage.

The individual had hemophilia A with inhibitors and had previously completed the ...