Ninety-two percent of patients who bled during the run-in period of Hemab’s Phase 2 study saw reductions in treated bleed rates on sutacimig, a figure that quietly reframes what subcutaneous prophylaxis could mean for a disease where, until now, patients have largely managed acute events with on-demand IV therapy. The Phase 2 long-term extension data, presented at ISTH 2026 in Paris, cover 34 patients at a median 6.9 months of exposure, with some extending to 15.9 months. That duration matters: it’s long enough to distinguish a durable prophylactic effect from a honeymoon response, and FDA has accepted the clinical package as sufficient to proceed to Phase 3 with a 0.2 mg/kg weekly dose.
The granular bleed data reinforce why the weekly regimen was selected. In the low-dose weekly cohort specifically, mean annualized treated bleed rate fell by approximately 84%. Among participants who had experienced high-intensity bleeding events, defined as those requiring transfusions, recombinant Factor VIIa, or hospitalization in the 12 months before sutacimig, the mean rate dropped 62% over the treatment and extension period. Three participants also underwent invasive procedures on study, all with successful hemostatic outcomes, providing the first surgical-use signal in this population. The safety picture is not without complexity: three participants experienced Grade 2 thromboembolic events, all in higher-exposure cohorts or in patients with multiple concurrent risk factors, and all resolved or were resolving at the data cut. The FDA-aligned Phase 3 dose was explicitly chosen to optimize bleed reduction while avoiding the peak exposures associated with those events in Phase 1/2.
Hemab is simultaneously pushing sutacimig into Factor VII deficiency, where preclinical data show restoration of thrombin generation under disease-mimicking conditions and confirmed binding across 88% of tested variants, covering the practical breadth of a genetically heterogeneous patient population. The natural history data presented alongside the trial results do important contextual work: GT360 data from 117 patients show that over 90% of pediatric and adolescent patients bleed at least weekly, and 72% of those aged 40 and older still report weekly bleeds. In the ATHN Transcends cohort, only 14% of patients received any prophylaxis, and 44% of bleeds went untreated entirely. Approved options for prophylaxis in GT remain limited, and the psychological toll documented, including depressive symptom prevalence running three to four times that of the general population, adds clinical urgency that bleed counts alone cannot capture.
Phase 3 initiation is planned for the second half of 2026. The single number worth tracking from here is the annualized treated bleed rate in the weekly 0.2 mg/kg cohort once Phase 3 data mature: if that approximately 84% reduction holds in a larger, more diverse population, it will define the evidentiary floor for any subsequent entrant in this space.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
