Pfizer Inc. announced significant findings from its Phase 3 BASIS study, revealing that HYMPAVZI® (marstacimab) dramatically reduces bleeding episodes in adults and adolescents with hemophilia A or B who develop inhibitors. The study reported a remarkable 93% reduction in key bleeding outcomes compared to traditional on-demand treatments using bypassing agents. These results were presented at the 67th American Society of Hematology Annual Meeting in Orlando and also published in the journal Blood.
HYMPAVZI offers a user-friendly treatment option, requiring only a once-weekly subcutaneous injection that involves minimal preparation and eliminates the need for treatment-related laboratory monitoring. Inhibitors are antibodies that can neutralize factor replacement therapies, making them ineffective for patients living with hemophilia. Of the approximately 800,000 individuals globally affected by hemophilia A or B, around 20% of those with hemophilia A and 3% of those with hemophilia B develop inhibitors that hinder effective treatment.
Dr. Davide Matino, Principal Investigator of the BASIS study and Associate Professor of Medicine at McMaster University, emphasized the impact of inhibitors: “The emergence of inhibitors poses significant treatment challenges and can increase disease burden for people living with hemophilia A or B. This study demonstrates HYMPAVZI’s potential as a safe and efficacious treatment option that not only significantly reduced bleeding episodes via a once-weekly subcutaneous administration but also showed improvement in certain aspects of health-related quality of life.”
The BASIS trial involved 48 participants diagnosed with severe hemophilia A or B with inhibitors, who were treated with HYMPAVZI for a 12-month active treatment phase following a six-month observational period using on-demand intravenous bypassing agents. Participants initially received a 300 mg subcutaneous loading dose of HYMPAVZI, followed by a weekly 150 mg dose.
Safety data from the study indicated that HYMPAVZI was generally well tolerated. Among the 51 participants in the safety population, there were no reports of deaths or thromboembolic events. 38 patients experienced adverse events (AEs) during the active treatment phase, with the most common being COVID-19 (21.6%), upper respiratory tract infections (15.7%), fibrin D-dimer increases (9.8%), and headaches (9.8%). Most AEs were classified as mild or moderate, although one serious AE related to treatment—skin rash—was reported, leading to study discontinuation but was subsequently resolved.
Dr. Michael Vincent, Chief Inflammation & Immunology Officer at Pfizer, expressed optimism regarding the findings: “It is encouraging that these data demonstrate the potential of HYMPAVZI to combine efficacy, safety, and straightforward administration for adults and adolescents living with hemophilia A or B with inhibitors and address a significant patient need. We look forward to potentially making this treatment available for these patients as Pfizer continues its ongoing effort spanning over 40 years to improve hemophilia care.”
Pfizer has submitted the findings to the U.S. Food and Drug Administration and the European Medicines Agency for review. Currently, HYMPAVZI is approved in more than 40 countries for the treatment of eligible patients aged 12 years and older with hemophilia A without factor VIII inhibitors or hemophilia B without factor IX inhibitors.
The BASIS study serves as a pivotal investigation into the efficacy and safety profile of HYMPAVZI, involving a diverse population of patients with severe hemophilia A (defined as FVIII <1%) or moderately severe to severe hemophilia B (defined as FIX activity ≤2%). This comprehensive research highlights the pressing need for effective treatments in patients facing the challenges of inhibitor development, paving the way for advancements in hemophilia management.
