Pfizer Inc. has shared promising results from its pivotal Phase 3 BASIS clinical trial of marstacimab, a potential new treatment for individuals with severe hemophilia A and moderately severe to severe hemophilia B, who do not have inhibitors to coagulation Factors VIII or IX. These findings were presented at the 65th American Society of Hematology (ASH) Annual Meeting and Exposition in San Diego.
The BASIS trial included 116 participants with hemophilia, comparing a 12-month active treatment period (ATP) with marstacimab to a six-month observational period where patients received routine prophylaxis (RP) or on-demand (OD) treatment with intravenous infusions of FVIII or FIX. Marstacimab, an innovative anti-tissue factor pathway inhibitor (anti-TFPI), was given as a subcutaneous 300 mg loading dose followed by 150 mg weekly injections.
The trial’s results were highly encouraging, demonstrating a statistically significant and clinically meaningful reduction in the annualized bleeding rate (ABR) during the treatment with marstacimab, with the reduction being maintained in long-term follow-up. These outcomes may offer a future subcutaneous treatment alternative that could notably reduce bleeding risks in hemophilia patients, as opposed to the frequent intravenous infusions currently in use.
Marstacimab’s safety profile was consistent with earlier Phase 1/2 results, showing general tolerability and no reports of deaths, thromboembolic events, or consumptive coagulopathy in the clinical trials. Most common adverse events included COVID-19, hemorrhages, liver disorders, hypersensitivity reactions, increased blood pressure, and injection site reactions. There was one treatment-related serious adverse event (peripheral swelling) and a single discontinuation due to a non-treatment-related serious adverse event.
Dr. James Rusnak from Pfizer highlighted the potential of the drug to deliver efficacy and safety through subcutaneous injections—a significant improvement over current methods. Dr. Davide Matino from McMaster University also noted the trial’s results, emphasizing the reduced burden of treatment with weekly subcutaneous injections and low monitoring needs.
Pfizer’s commitment to addressing the needs of hemophilia patients is evident with three Phase 3 programs investigating novel treatments, indicating their ongoing contribution to the advancement of hemophilia therapies.