Pfizer disclosed a death in a clinical trial of its tissue factor pathway inhibitor (TFPI) antagonist Hympavzi (marstacimab) after a cerebellar infarction followed by cerebral hemorrhage, prompting scrutiny from clinicians and regulators. The company notified the hemophilia community and placed the long‑term extension participant’s case under review; details on whether the event is drug‑related remain pending. The incident raises broader safety questions for TFPI antagonists and other novel hemostasis modulators as companies balance bleeding and thrombotic risks in hemophilia development programs.