Omeros announces update on statistical analysis of narsoplimab primary endpoint

Omeros (OMER) announced statistical sensitivity analysis results related to the primary endpoint analysis for narsoplimab, Omeros’ monoclonal antibody inhibiting the lectin pathway of complement, in the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy, a life-threatening complication in both adult and pediatric hematopoietic stem cell transplantation. The sensitivity analyses, conducted by an independent statistical group, demonstrate the robustness of the results of the previously reported primary endpoint analysis, with representative hazard ratios ranging from 0.24 to 0.42 and p-values ranging from less than 0.00001 to 0.0124. As reported on December 19, 2024, narsoplimab met its primary endpoint, with TA-TMA patients in its OMS721-TMA-001 pivotal trial demonstrating clinically meaningful and statistically significant superiority in overall survival – a hazard ratio of 0.32 with p-value less than 0.00001 – compared to the TA-TMA registry patients. The hazard ratio of 0.32 indicates that the narsoplimab-treated TA-TMA patients had an over three-fold reduction in risk of mortality. Across all its clinical trials in various indications to date, narsoplimab has been well tolerated and has shown no safety signal of concern. Prior to the independent statistical group conducting any narsoplimab analyses, Omeros had received and incorporated FDA’s recommendations on the statistical analysis plan for the primary analysis and sensitivity analyses comparing overall survival from time of first dosing in the 28 narsoplimab-treated TA-TMA patients in OMS721-TMA-001 to overall survival, adjusted for immortal time bias, of the more than 100 TA-TMA patients in the external control registry, none of whom received narsoplimab. The two cohorts had similar demographics, diagnostic criteria, baseline characteristics, underlying diseases, conditioning regimens, and transplant procedures. All patients in both cohorts met the published criteria for high risk of death as defined by an international expert panel tasked with reaching consensus on diagnostic and prognostic criteria and representing the American Society for Transplantation and Cellular Therapy, the Center for International Bone Marrow Transplant Research, the Asia-Pacific Blood and Marrow Transplantation Group, and the European Society for Blood and Marrow Transplantation. While awaiting the results from the expanded access program-related analyses, international groups of transplant experts have begun preparing two manuscripts – one directed to primary endpoint analyses and the other to EAP-related analyses – for submission to peer-reviewed journals.