The European Commission has approved Pfizer’s Hympavzi (marstacimab) for hemophilia A and B patients with inhibitors. The approval means Pfizer is one of few companies offering a once-weekly subcutaneous option that covers both hemophilia subtypes in the inhibitor-positive population — a segment historically underserved by approved prophylactic therapies.
The EC granted marketing authorization expanding Hympavzi’s approved indication to patients 12 years of age and older weighing at least 35 kg with hemophilia A (congenital factor VIII deficiency) with FVIII inhibitors, or hemophilia B (congenital factor IX deficiency) with FIX inhibitors. The authorization is valid across all 27 EU member states, as well as Iceland, Liechtenstein, and Norway. Pfizer said no routine treatment-related laboratory monitoring is required for this population under the approved regimen.
Clinical evidence from the BASIS trial
The indication extension rests on data from the Phase III BASIS trial (NCT03938792), a global, open-label, multicenter study evaluating marstacimab in adolescents and adults aged 12 to under 75 years with severe hemophilia A or moderately severe to severe hemophilia B with or without inhibitors. The inhibitor cohort included 48 participants treated during a 12-month active treatment period, compared against a six-month observational period on on-demand bypass therapy. The primary endpoint was the treated annualized bleeding rate during the active treatment period. Marstacimab produced a 93% reduction in mean treated annualized bleeding rate versus on-demand therapy (1.39 versus 19.78; p<0.0001), with superiority also demonstrated across secondary bleeding endpoints including spontaneous, joint, and target joint bleeds. An interim analysis of an open-label extension study, covering up to 41 additional months of treatment, showed mean and median treated annualized bleeding rates remained low, with a median of 0.00.
Scientific context and competitive landscape
Inhibitors — neutralizing antibodies that develop against factor replacement therapies — affect approximately 20% of people with hemophilia A and 3% of those with hemophilia B, rendering standard factor concentrates ineffective and substantially narrowing prophylactic options. Hympavzi targets tissue factor pathway inhibitor (TFPI), specifically its Kunitz 2 domain, through a mechanism distinct from factor replacement: rather than supplying deficient clotting factors, the drug reduces TFPI-mediated suppression of coagulation initiation, aiming to rebalance hemostasis regardless of the underlying factor deficiency.