Pfizer disclosed a fatality in a long‑term extension trial of its tissue factor pathway inhibitor antagonist Hympavzi, reporting a cerebellar infarction followed by cerebral hemorrhage in a participant. The company notified the hemophilia community and regulators, and the event is under review. Pfizer’s letter to stakeholders raised questions about safety monitoring in extended exposure studies for hemostasis agents. The disclosure has led to renewed scrutiny of trial design, adverse‑event attribution, and risk‑mitigation measures in bleeding disorder drug development. Regulators and clinicians will monitor the investigation outcome and any recommended protocol or label changes; sponsors running long‑term extension studies may reassess monitoring plans and informed consent language in light of the event.