Pfizer Highlights Phase 3 Trial Results of Marstacimab

Marstacimab is a laboratory-engineered monoclonal antibody developed to treat hemophilia A and B patients, with or without inhibitors.

Pfizer has announced positive results from their global phase 3 BASIS clinical study of marstacimab, the company’s investigational, subcutaneous therapy that targets an anticoagulant protein known as tissue factor pathway inhibitor (TFPI).

Marstacimab is a laboratory-engineered monoclonal antibody developed to treat hemophilia A and B patients, with or without inhibitors. It works by blocking and effectively preventing TFPI from performing the anticoagulant function that it naturally carries out in the human body. This type of therapy allows treaters to forgo the need for traditional factor replacement.

BASIS is evaluating annualized bleed rate (ABR) through one year of treatment with marstacimab in approximately 145 adolescent and adult participants between ages 12 to 75 years with severe hemophilia A or B, with or without inhibitors.

According to the Pfizer update, prophylactic therapy with marstacimab resulted in a “statistically significant and clinically relevant” reduction in ABR in people living with severe hemophilia A and moderately severe to severe hemophilia B without inhibitors.

To date, 116 trial participants have been treated with marstacimab during a 12-month period versus a prophylaxis and on-demand intravenous regimen with FVIII or FIX replacement therapy administered as part of routine care in a six-month lead-in period. In the group of patients treated with on-demand factor replacement intravenous therapy in the lead-in period, marstacimab demonstrated superiority with a 92% reduction in bleeds. The results also showed superiority  with marstacimab compared to prophylaxis, with a 35% reduction in ABR.

In terms of safety, the company reported a profile that was consistent with phase 1/2 results as treatment was generally well-tolerated. No deaths, thromboembolic events or consumptive coagulopathy (widespread hypercoagulable state) events were reported.

“Despite significant treatment advances in recent years, many people living with hemophilia unfortunately continue to experience bleeding episodes and are required to manage their disease with frequent intravenous infusions,” said Chris Boshoff, MD, PhD, Chief Development Officer, Oncology and Rare Disease, Pfizer Global Product Development. “These results support the potential for marstacimab to become the first once-weekly non-factor treatment for people with hemophilia B and a treatment option that helps address the diverse needs of patients with hemophilia A or B without inhibitors. These needs include preventing excessive or potentially life-threatening bleeds, while at the same time reducing the burden of treatment with once-weekly, subcutaneous administration.”

Source: Pfizer press release dated May 30, 2023, National Hemophilia Foundation