An Update From the Pfizer Hemophilia Team

Dear Hemophilia Community Partners,

On December 22, 2025, we shared the very sad news of the passing of a hemophilia A
participant with inhibitors in the marstacimab long-term extension trial. We remain
committed to transparency as we continue to assess what occurred.

The circumstances of this case are multi-factorial – including co-existing conditions, the
participant undergoing a urethroscopic surgical procedure, and use of a bypassing agent as
a concomitant therapy – and we are working to understand these elements as fully as
possible in this clinical setting. We plan to present this information as part of a late-breaker
session at the EAHAD congress on February 6.

As we previously shared, an independent external Data Monitoring Committee oversees all
ongoing marstacimab studies. Based on the current information available, the studies are
continuing as planned and the established benefit/risk profile of marstacimab remains
unchanged. We are continuing to review and assess information on this case as we always
do for our medicines, per established processes.

Thank you for your partnership and for your commitment to the hemophilia community.
​
Sincerely,
The Pfizer Hemophilia Team