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Key takeaways
Strong Prophylactic Efficacy: Hympavzi achieved a 93% reduction in annualized bleeding rate versus on-demand treatment in patients with hemophilia A or B with inhibitors.
Operational Simplicity: Once-weekly subcutaneous dosing with a pre-filled pen offers a less burdensome administration route for sites and patients.
Clear Trial Design and Endpoints: The BASIS trial highlights the value of well-structured, open-label studies with clearly defined primary and secondary endpoints in driving regulatory approval and adoption.
Pfizer has shared positive data from its Phase III BASIS clinical trial (NCT03938792) of Hympavzi (marstacimab) for adults and adolescents living with hemophilia A or B with inhibitors. The study met its primary endpoint along with other key secondary measures by demonstrating that subcutaneous Hympavzi improved a number of bleeding outcomes compared to on-demand treatment.1
In a press release, Davide Matino, MD, MSc, BASIS principal investigator, associate professor of medicine, McMaster University, said: “Patients with inhibitors tend to face frequent complications, and navigating the treatment landscape can introduce complexities and increase disease burden The strong bleed reduction with Hympavzi compared to on-demand treatment in the Phase III BASIS study, coupled with its weekly administration method, offers exciting potential for these patients who are in critical need of treatment options.”
Hympavzi reduces annualized bleeding rate by 93%
- In the BASIS study, prophylactic treatment with Hympavzi demonstrated a statistically significant and clinically relevant reduction in annualized bleeding rate (ABR) of treated bleeds in patients living with severe hemophilia A or hemophilia B with inhibitors.
- Hympavzi outperformed on-demand treatment by achieving a 93% reduction in ABR over 12 months.
- BASIS also demonstrated positive results across a number of bleeding-related secondary endpoints including spontaneous bleeds, joint bleeds, target joint bleeds, and total bleeds.
BASIS study design and patient population
- The BASIS trial is a Phase III, open-label, multicenter study evaluating the safety and efficacy of Hympavzi in adolescent and adult participants with severe hemophilia A or moderately severe to severe hemophilia B,
- The cohort of BASIS highlighted in this announcement included 48 participants living with hemophilia with inhibitors.
- These patients were treated with Hympavzi during a 12-month active treatment period (ATP) versus an on-demand intravenous regimen with bypassing agents, administered as part of routine care in a six-month observational period.
- During the ATP, patients first received prophylaxis (a 300 mg subcutaneous loading dose of Hympavzi, followed by 150 mg subcutaneously once weekly) with potential for a dose escalation to 300 mg once weekly.
- Additionally, three patients in the inhibitor cohort were on routine prophylactic treatment before entering the study and were not included in the primary efficacy analysis.
In the press release, Michael Vincent, MD, PhD, chief inflammation & immunology officer, Pfizer, added: “These encouraging results demonstrate Hympavzi’s potential to help people living with hemophilia A or B with inhibitors, meeting an important need for patients with antibodies that neutralize most factor-based prophylactic options used to manage bleeding episodes. Hympavzi represents Pfizer’s latest contribution in more than 40 years of working to advance hemophilia care, as a generally well-tolerated treatment option that could offer bleed protection with a straightforward, once-weekly subcutaneous administration in a pre-filled pen for patients with inhibitors, if approved in this patient population.”
While these positive results represent a win for a patient population in need of less burdensome treatment approaches, Pfizer noted that analysis of the full Phase III dataset from the inhibitor cohort is still ongoing and expects to present additional outcomes at upcoming medical meetings.
Earlier FDA approval expands access to Hympavzi
Hympavzi was approved by the FDA earlier in October 2024 for routine prophylaxis to prevent or reduce the frequency of bleeding episodes in patients 12 years of age and older with hemophilia A (congenital factor VIII deficiency) without factor VIII inhibitors, or hemophilia B (congenital factor IX deficiency) without factor IX inhibitors.2
With its approval, the rebalancing agent became the first and only anti-tissue factor pathway inhibitor approved in the US for the treatment of hemophilia A or B. Additionally, it became the first hemophilia medicine approved in the US to be administered by a pre-filled, auto-injector pen.
This approval was based on earlier positive results from the BASIS study, which represented a different class of patients with both hemophilia A or B. In the trial, Hympavzi lowered the ABR for treated bleeds by 35% and 92% after a 12-month ATP.
References
1. Pfizer Announces Positive Topline Phase 3 Results for HYMPAVZI™ in Hemophilia A or B with Inhibitors. News release. Pfizer. June 26, 2025. Accessed June 26, 2025. https://www.businesswire.com/news/home/20250626097323/en/Pfizer-Announces-Positive-Topline-Phase-3-Results-for-HYMPAVZI-in-Hemophilia-A-or-B-with-Inhibitors
2. U.S. FDA Approves Pfizer’s HYMPAVZI™ (marstacimab-hncq) for the Treatment of Adults and Adolescents with Hemophilia A or B Without Inhibitors. News release. Pfizer. October 11, 2024. Accessed June 26, 2025. https://www.businesswire.com/news/home/20241009505480/en/U.S.-FDA-Approves-Pfizers-HYMPAVZI-marstacimab-hncq-for-the-Treatment-of-Adults-and-Adolescents-with-Hemophilia-A-or-B-Without-Inhibitors