FDA Expands Marstacimab Indication in Hemophilia A and B - Summary - MDSpire

FDA Expands Marstacimab Indication in Hemophilia A and B

Phase 3 BASIS and BASIS KIDS data supported the expanded indication across pediatric and inhibitor-pretreated populations.

  • By

  • Kathryn Wighton

  • June 8, 2026

  • 3 min

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Objective:

To report the FDA's approval of an expanded indication for marstacimab-hncq (HYMPAVZI) for routine prophylaxis in hemophilia A and B patients.

Key Findings:
  • In the BASIS trial, marstacimab reduced the mean treated annualized bleeding rate (ABR) by 93% compared to on-demand treatment.
  • Mean treated ABR was 1.4 for marstacimab versus 19.8 for on-demand treatment (p<0.0001).
  • In BASIS KIDS, mean treated ABR was 1.8 for patients without inhibitors and 1.4 for those with inhibitors, compared to historical rates of 3.6 and 18.9, respectively.
Interpretation:

Marstacimab targets the Kunitz 2 domain of tissue factor pathway inhibitor (TFPI) to restore balance between bleeding and coagulation.

Limitations:
  • Interim results from BASIS KIDS are descriptive analyses and not inferential comparisons.
  • Reference rates in BASIS KIDS are historical model-based estimates.
Conclusion:

Marstacimab is the first subcutaneous non-factor therapy available for pediatric patients with hemophilia B aged 6 to 11 years.

Original Source(s)

FDA Expands Marstacimab Indication in Hemophilia A and B

  • by Kathryn Wighton

  • June 8, 2026

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