Pfizer recently announced results from a clinical study which is currently evaluating HYMPAVZI™ (marstacimab-hncq) for adults and adolescents living with hemophilia A or B with inhibitors. The therapy was approved by the U.S. Food and Drug Administration in the fall of 2024 for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in adults and pediatric individuals 12 years of age and older with hemophilia A without factor VIII inhibitors, or hemophilia B without factor IX inhibitors. 

Marstacimab-hncq is a laboratory-engineered monoclonal antibody that targets an anticoagulant protein known as tissue factor pathway inhibitor (TFPI). It works by blocking and effectively preventing TFPI from performing the anticoagulant function that it naturally carries out in the human body.

According to a Pfizer press release, the phase 3 trial known as BASIS, demonstrated that prophylactic treatment with marstacimab-hncq resulted in a "statistically significant and clinically relevant reduction” in annualized bleeding rate (ABR) of treated bleeds in people living with severe hemophilia A or hemophilia B with inhibitors. 

All 48 people with hemophilia in the phase 3 BASIS study were treated once per week with subcutaneous infusions of marstacimab-hncq during a 12-month period. This was compared with a six-month lead-in period when patients were treated on-demand with intravenous infusions of bypassing agents as part of their regular care. The topline results showed that marstacimab-hncq achieved a 93% reduction in ABR over 12 months (1.39 ABR with marstacimab-hncq vs 19.78 ABR with the on-demand regimen). Favorable results were also seen across other endpoints relevant to spontaneous bleeds, joint bleeds, target joint bleeds, and total bleeds.

“Patients with inhibitors tend to face frequent complications, and navigating the treatment landscape can introduce complexities and increase disease burden,” said Davide Matino, MD, MSc, BASIS Principal Investigator, Associate Professor of Medicine, McMaster University in Ontario, Canada. “The strong bleed reduction with HYMPAVZI compared to on-demand treatment in the Phase 3 BASIS study, coupled with its weekly administration method, offers exciting potential for these patients who are in critical need of treatment options.”

Source: Pfizer press release dated June 26, 2025

Editor’s Note: Watch this NBDF Wednesday Webinar to learn more about marstacimab-hncq.

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