Omeros Corporation (Nasdaq: OMER) said the European Medicines Agency's Committee for Medicinal Products for Human Use (CHMP) has adopted a negative opinion on the company's marketing authorization application for narsoplimab in the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA).

The decision followed an oral explanation meeting at which Omeros presented its position alongside four international experts in hematopoietic cell transplantation. Omeros said it intends to request a re-examination of the CHMP opinion and will seek review by an Ad Hoc Expert Group, an independent panel of external scientific and clinical experts to be convened by the EMA.

Narsoplimab, sold under the brand name Yartemlea, was approved by the U.S. Food and Drug Administration in December 2025 for the treatment of TA-TMA in adults and children two years of age and older. The European application was supported by data from Omeros' pivotal clinical trial, survival analyses comparing narsoplimab-treated patients to an external patient registry, and data from the company's compassionate use program — the same data set used by the FDA in its approval decision.

"We are disappointed by the CHMP's opinion, particularly given the lethal nature of TA-TMA, the absence of an approved treatment for this condition in Europe, and the totality of the clinical trial and real-world data supporting narsoplimab's efficacy and safety," said Gregory A. Demopulos, M.D., chairman and chief executive officer of Omeros.

Omeros said it plans to continue providing Yartemlea to TA-TMA patients in Europe through its global compassionate use program while the regulatory review process continues. The company noted that compassionate use access in Europe is limited due to drug supply and access constraints.

TA-TMA is a severe complication of hematopoietic stem cell transplantation. Mortality in severe cases can exceed 90%, according to the company's press release. Approximately 30,000 allogeneic transplants are performed annually in the U.S. and Europe combined, with recent studies estimating TA-TMA develops in up to 56% of allogeneic transplant recipients.