Marstacimab for mild to moderate hemophilia A or B in people without inhibitors
Official title: AN OPEN-LABEL STUDY TO EVALUATE THE EFFICACY AND SAFETY OF MARSTACIMAB PROPHYLAXIS IN ADOLESCENT AND ADULT PARTICIPANTS WITH MILD (FVIII OR FIX ACTIVITY >5% TO ≤15%) TO MODERATE (≥1% TO ≤5%) HEMOPHILIA A OR B WITHOUT INHIBITORS
Run by Pfizer · NCT07923981 · Data updated 2026-11-12
This study tests whether weekly injections of marstacimab can reduce bleeding in adolescents and adults with mild to moderate hemophilia A or B who don’t have inhibitors.
Quick facts
| Phase | Phase 3 |
|---|---|
| Study type | Interventional |
| Ages | 12 Years to 74 Years |
| Sex | All |
| Enrollment | 95 (estimated) |
| Sponsor | Pfizer Industry-sponsored |
| Drugs / interventions | marstacimab |
| Locations | 1 site (Flowood, Mississippi) |
| Status | Recruiting |
| Started | October 23, 2026 |
| Main results expected | July 2, 2029 |
| Study ends | June 16, 2032 |
| Registry record updated | November 9, 2026 |
| Trial ID | NCT07923981 on ClinicalTrials.gov |
Is this trial a fit for you?
✓Likely a good fit
Individuals aged 12 to less than 75 years with mild to moderate hemophilia A or B (factor activity >1% to ≤15%), no history of inhibitors in the past 5 years, and documented prior bleeding despite factor therapy.
✕Probably not a fit
Patients with inhibitors, very severe disease outside the eligible activity ranges, or those lacking adequate historical records may not benefit or qualify.
A plain-English reading of the study's rules. Only the study team can confirm whether you qualify.
What this trial studies
This open-label, multicenter Phase 3 trial evaluates the safety and efficacy of marstacimab given as a 150 mg weekly subcutaneous dose for 12 months in people aged 12 to under 75 with mild to moderate hemophilia A or B and no inhibitors. Participants will be grouped by their prior bleeding treatment (on-demand vs routine prophylaxis) to compare historical bleeding on factor replacement with outcomes during marstacimab treatment. Key endpoints include bleeding events and other efficacy measures, alongside safety assessments. Eligibility requires specific factor activity ranges, prior bleeding history, and stable records of treatment or diary data, with additional considerations for females with severe disease on a case-by-case basis.
Why it matters
Potential benefit: If successful, marstacimab could reduce bleeding events and improve quality of life for people with mild to moderate hemophilia A or B who have ongoing bleeding despite conventional therapy.
How similar studies have gone: Habituation to similar pro-phyxis agents in hemophilia has shown potential reductions in bleeding, though results vary and this exact approach is being tested in this trial.
Who can join: the full rules
Show full inclusion / exclusion criteria
Inclusion Criteria * Male or female, 12 to less than 75 years of age and weighing at least 35 kg. * Moderate hemophilia A or B (factor VIII or factor IX activity ≥1% to ≤5%), or Mild hemophilia A or B (factor VIII or factor IX activity \>5% to ≤15%). * Females with severe hemophilia A or B may be eligible on a case-by-case basis following discussion with sponsor. * No history of factor VIII or factor IX inhibitors within the 5 years before screening. * At least 12 months of medical records and/or bleeding diary data documenting hemophilia-related bleeding episodes and factor VIII or factor IX replacement therapy prior to screening. * Participants receiving on-demand factor replacement therapy must have had at least 2 treated bleeding episodes during the 12 months before screening (surgical or procedural bleeds do not count). * Participants receiving routine prophylactic factor replacement therapy must have received a stable prophylaxis regimen for at least 12 months with ≥80% compliance and at least 1 treated bleeding episode in the 12 months before screening (excluding surgical or procedural bleeds). Exclusion Criteria * Current evidence of a congenital or acquired thrombophilic disorder, including antithrombin III deficiency, Factor V Leiden mutation, prothrombin G20210A mutation, protein C deficiency, protein S deficiency, or antiphospholipid syndrome. * Known coronary artery disease, history of venous or arterial thrombosis, or other clinically significant ischemic disease. * Any bleeding disorder other than hemophilia A or hemophilia B. * Any medical, psychiatric, or laboratory abnormality that, in the investigator's opinion, could increase risk or interfere with study participation. * Current use of bypassing agents, non-factor replacement therapies for hemophilia, or prior hemophilia gene therapy. * Regular treatment with immunomodulatory medications. * Use of prohibited medications, including systemic antifibrinolytic agents, medications that increase bleeding risk, or certain nonsteroidal anti-inflammatory drugs (NSAIDs), as specified by the protocol. * Use of estrogen-containing hormonal therapies (including contraceptives and HRTs) within 30 days before or during the study, or depot medroxyprogesterone acetate within 6 months before or during the study. * Receipt of another investigational drug or vaccine within 30 days or 5 half-lives before study treatment (whichever is longer), or planned participation in another investigational study during this study. * Significant renal or hepatic impairment or clinically significant laboratory abnormalities at screening. * Platelet count \<100,000/μL, hemoglobin \<10 g/dL (with limited exceptions), fibrinogen below the lower limit of normal, or prolonged prothrombin time. * CD4 count ≤200 cells/μL in participants with HIV infection. * Clinically significant electrocardiogram abnormalities at screening. * Planned surgical procedure during the study period. * Known hypersensitivity to hamster protein or any component of the study treatment. * Study site personnel, sponsor personnel directly involved in the conduct of the study, or their immediate family members.
Where it's running
-
Southern Specialty Clinic
Flowood, Mississippi, United States Recruiting
Study contacts
- Study coordinator: Pfizer CT.gov Call Center
- Email: ClinicalTrials.gov_Inquiries@pfizer.com
- Phone: 1-800-718-1021
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How to take part
- Review the eligibility criteria above with your treating physician.
- Check the official listing on ClinicalTrials.gov for the latest contact details and recruitment status.
- Contact the study coordinator or principal investigator to ask for pre-screening. Pre-screening is free and never obligates you to enroll.