Message from the Pfizer Hemophilia Team

Dear Hemophilia Community Partners, 

We are deeply saddened to share that a participant in the long-term extension trial  (B7841007) studying marstacimab in people living with hemophilia A or B with or without inhibitors has passed away in December 2025 following serious adverse events of  cerebellar infarction and subsequent cerebral hemorrhage. On behalf of everyone at Pfizer,  we extend our heartfelt sympathies to the participant’s family, friends, and all those  involved in their care. 

Pfizer, together with the trial investigator and the independent external Data Monitoring  Committee, are actively gathering information to better understand the complex, multi factorial circumstances surrounding this occurrence – including co-existing medical  conditions and concomitant medications – and the causality of the event. The individual, a  patient with hemophilia A and inhibitors, participated in the active treatment phase of the  parent study (B7841005) in 2022 prior to entering the long-term extension study in 2023.  Regulatory authorities and investigators have been informed. 

The safety and well-being of participants in our clinical trials remain our highest priority,  and we are committed to transparency and keeping the community informed as we learn  more. 

​Sincerely, 
​The Pfizer Hemophilia Team