Orlando, December 8, 2025 — Leads & Copy — Pfizer Inc. (NYSE: PFE) presented results from the Phase 3 BASIS study, demonstrating the superiority of HYMPAVZI® (marstacimab) in improving bleeding outcomes for adults and adolescents with hemophilia A or B with inhibitors, compared to on-demand treatment with bypassing agents.
The findings were shared in an oral presentation at the 67th American Society of Hematology (ASH) Annual Meeting and Exposition in Orlando and published in Blood.
HYMPAVZI, a treatment for hemophilia, has shown positive results in a Phase 3 study. It is currently approved in over 40 countries for eligible patients 12 years of age and older living with hemophilia A without factor VIII inhibitors, or hemophilia B without factor IX inhibitors. The study (NCT03938792) evaluated the efficacy of HYMPAVZI in adults and adolescents living with hemophilia A or B with inhibitors, which are antibodies that neutralize factor replacement therapies. Approximately 20% of people with hemophilia A and 3% of people with hemophilia B develop inhibitors, rendering factor replacement therapies ineffective.
In the BASIS trial, 48 adults and adolescents with severe hemophilia A or B with inhibitors were treated with HYMPAVZI during a 12-month active treatment phase (ATP). This followed a six-month observational phase of on-demand (OD) intravenous regimen with bypassing agents, part of their usual care. During the ATP, participants received HYMPAVZI as a 300 mg subcutaneous loading dose, followed by once-weekly 150 mg dosing. The study revealed a statistically significant and clinically meaningful 93% reduction in mean treated annualized bleeding rate (ABR), with 1.39 compared to 19.78 with OD therapy (p<0.0001). These results remained consistent across different types of hemophilia, ages, and geographic locations.
The study also found a median ABR of 0 with HYMPAVZI, compared to 16.42 with OD treatment. HYMPAVZI also demonstrated superiority across all bleeding-related secondary endpoints, including spontaneous bleeds, joint bleeds, target joint bleeds, and total treated and untreated bleeds (p<0.0001). Health-related quality-of-life outcomes improved with HYMPAVZI after six months in the ATP, as demonstrated by a median difference of -25.9 in the Haem-A-QoL physical health domain (p<0.0001), a median difference of -13.5 in the Haem-A-QoL total score (p<0.0001), and a median difference of 0.1043 in the EQ-5D-5L index score (p<0.0377).
HYMPAVZI was generally well tolerated during the trial. There were no deaths or thromboembolic events reported in the 51 participants included in the safety population. Adverse events (AEs) were reported by 38 patients, with the most common being COVID-19 (21.6%), upper respiratory tract infection (15.7%), fibrin D-dimer increase (9.8%), and headache (9.8%). Most AEs were mild or moderate in severity. One serious AE, a treatment-related skin rash, was reported, which led to study discontinuation but was later resolved.
Pfizer has submitted these data to the U.S. Food and Drug Administration and European Medicines Agency for review.
HYMPAVZI is intentionally designed to target tissue factor pathway inhibitor (TFPI) and was the first anti-TFPI approved in the U.S. and EU for the treatment of hemophilia A or B. HYMPAVZI is administered via a pre-filled, auto-injector pen and offers a once-weekly subcutaneous dosing schedule with minimal preparation required for each administration.
Pfizer is also conducting BASIS KIDS, an open-label study investigating the safety and efficacy of HYMPAVZI in children up to <18 years of age with severe hemophilia A or moderately severe to severe hemophilia B with or without inhibitors.
Hemophilia is a rare genetic blood disease caused by a clotting factor deficiency, affecting more than 800,000 people worldwide. Approximately 20% of people with hemophilia A and 3% of people with hemophilia B develop inhibitors, leading to higher treatment burdens and potential complications.
Important Safety Information: Before using HYMPAVZI, patients should consult their healthcare provider about factor VIII and factor IX products and should promptly seek medical attention for signs and symptoms of blood clots or allergic reactions.
Common side effects include injection site reactions, headache, and itching.
Source: Pfizer Inc.
