FDA Approves First Treatment for HSCT-Associated Thrombotic Microangiopathy

YARTEMLEA is the first and only approved lectin pathway inhibitor. YARTEMLEA selectively inhibits MASP-2, the effector enzyme of the lectin pathway, blocking pathway activation while preserving classical and alternative complement functions important for host defense. YARTEMLEA is approved for use in adults and in children ages two years and older.

“This approval is a long-awaited breakthrough in hematopoietic cell transplantation and TA-TMA care,” stated Miguel-Angel Perales, M.D., Chief of the Adult Bone Marrow Transplantation Service at Memorial Sloan Kettering Cancer Center. “Until now, we’ve lacked an effective TA-TMA therapy and relied largely on supportive measures such as modifying calcineurin inhibitors, which can significantly increase the risk of life-threatening graft-versus-host disease. Based on a compelling data package, narsoplimab delivers robust response rates and improved survival in TA-TMA, with a favorable benefit-risk profile and a safety profile consistent with that seen in patients undergoing hematopoietic stem cell transplantation. As the first and only drug approved for TA-TMA, narsoplimab is a practice-changing advance for patients facing this devastating complication.”

Approval of YARTEMLEA was based on results from a single-arm, open-label study in adults with TA-TMA (the TA-TMA Study; N=28), supported by additional data from an expanded access program (EAP; N=221 adult and pediatric patients). In the EAP, 19 patients (13 adult and 6 pediatric) had evaluable patient-level response data.

Efficacy was assessed by TMA complete response (CR), defined as improvement in key laboratory markers of TMA (platelet counts and LDH levels) together with either improved organ function or transfusion independence. CR was achieved in 17/28 patients (61%) in the TA-TMA Study and 13/19 evaluable EAP patients (68%). Across the TA-TMA Study and the EAP, 100-day survival from the time of TMA diagnosis (based on all-cause mortality) was 73% (95% confidence interval CI: 52, 86) and 74% (95% CI: 48, 88), respectively. All patients met international harmonization criteria for high-risk TA-TMA, classifying each patient as having a poor prognosis and high risk of death.

In peer-reviewed publications, treatment with YARTEMLEA was associated with a three- to fourfold lower risk of mortality compared with an external control cohort.1 In the EAP, YARTEMLEA was used both as first-line therapy and in high-risk TA-TMA patients who had failed or discontinued one or more prior regimens, namely off-label complement inhibitors and/or defibrotide. In these previously refractory high-risk patients, YARTEMLEA was associated with 50 percent one-year survival, compared with historical one-year survival rates reported as less than 20 percent.2 3 4 5

“Just as in adults, YARTEMLEA’s indication to treat TA-TMA in children two years of age and older is tremendously important,” said Michelle Schoettler, M.D., Assistant Professor of Pediatric Oncology and Hematopoietic Cellular Therapy at Emory University. “Peer-reviewed clinical publications in TA-TMA have steadily advanced our understanding of the disease in children – its biology, diagnostic criteria, and increasing recognition – and have revealed the limitations and risks of relying on off-label options in this setting. Across the published pediatric experience, YARTEMLEA has produced strong and consistent benefit, including in very high-risk children with organ dysfunction and in those who have failed prior complement-inhibition therapy. When used first-line, YARTEMLEA has been associated with approximately 75 percent one-year survival; and even in children refractory to one or more off-label complement inhibitors, one-year survival is approximately triple historical rates that have remained below 20 percent. My clinical experience with YARTEMLEA through the expanded access program, including in very young patients, has reinforced that it needs to be readily available for children when TA-TMA emerges. With this approval, effective TA-TMA therapy can become the pediatric standard instead of the exception – and that will save children’s lives.”

All patients in the TA-TMA Study had multiple risk factors for poor outcomes, and adverse reactions were reported regardless of causality or relatedness to YARTEMLEA. The most common adverse reactions (≥20%) were viral infections, sepsis, hemorrhage, diarrhea, vomiting, nausea, neutropenia, pyrexia, fatigue, and hypokalemia. Serious adverse reactions occurred in 61% of YARTEMLEA-treated patients; those reported in >5% included acute kidney injury, confusional state, acute respiratory failure, neutropenic sepsis, septic shock, pulmonary edema, and vomiting. Fatal adverse reactions were reported in 7% of patients, including neutropenic sepsis and septic shock. No new clinically significant safety signals were identified in patients treated with YARTEMLEA in the EAP.

Following FDA approval of YARTEMLEA, Omeros is finalizing preparations for its U.S. product launch planned for January 2026. Dedicated U.S. billing and reimbursement codes are now in place, including:

• Diagnosis Code: ICD-10-CM code M31.11 specific to the diagnosis of “Hematopoietic Stem Cell Transplantation-Associated Thrombotic Microangiopathy”
• Procedure Codes: ICD-10-PCS codes XW03357 and XW04357 for introduction of narsoplimab monoclonal antibody into a peripheral vein or into a central vein, respectively

The YARTEMLEAssist™ patient support program is expected to be available in the first quarter of 2026. Providers and patient representatives can call 1-844-YARTEM1 (1-844-927-8361) for personalized services, including identifying potential financial assistance options.

“FDA’s approval of YARTEMLEA marks a defining milestone for Omeros and, more importantly, for patients and families facing TA-TMA,” said Gregory A. Demopulos, M.D., chairman and chief executive officer of Omeros. “After years of work and close collaboration with the transplant community, we can now offer the first FDA-approved therapy for this frequently fatal complication, with robust response data and a benefit-risk profile that supports confident use in both adults and children. With our U.S. launch planned for January 2026, our focus is on ensuring rapid, reliable access so that YARTEMLEA can be used when TA-TMA is recognized and time is critical. We are deeply grateful to the patients, caregivers, investigators, and clinical teams who made this approval possible, and we are committed to bringing YARTEMLEA to every eligible patient who needs it.”

TA-TMA can occur after both autologous and allogeneic hematopoietic stem cell transplantation, with higher prevalence following allogeneic transplant. Approximately 30,000 allogeneic transplants are performed each year in the U.S. and Europe. Recent studies estimate that TA-TMA develops in up to 56 percent of allogeneic transplant recipients.

A marketing authorization application for YARTEMLEA for the treatment of TA-TMA is currently under review by the European Medicines Agency with a decision expected in mid-2026.