Investing.com -- Shares of Omeros Corporation (NASDAQ: OMER) retreated 4% in Friday morning trading after the European Medicines Agency’s (EMA) Committee for Medicinal Products for Human Use (CHMP) maintained a negative opinion on the marketing authorization application for its drug, narsoplimab.

Following a formal re-examination, the CHMP rejected narsoplimab as a treatment for hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), reaffirming its initial negative stance from June 2026.

The regulatory decision follows a contested review process. As part of the re-examination, the CHMP convened an eight-member ad hoc expert group comprising hematologists, statisticians, transplant physicians, and patient representatives. According to the CHMP’s final minutes, this expert group recommended that external specialists review individual patient-level data to better understand factors driving treatment response and survival. While Omeros had submitted substantial patient-level data to the CHMP in August, the committee reportedly did not provide this data to the expert group prior to the decision.

This European rejection stands in stark contrast to the drug’s regulatory success in the United States. Narsoplimab was approved by the U.S. Food and Drug Administration (FDA) in December 2025 under the brand name YARTEMLEA. It remains the first and only FDA-approved therapy for TA-TMA in patients two years of age and older. The drug targets MASP-2, the effector enzyme of the complement system’s lectin pathway. Notably, it is the only systemic complement inhibitor on the market that does not require a boxed warning, a risk evaluation and mitigation strategy (REMS), or specific vaccinations.

Citing surging commercial demand for YARTEMLEA in the U.S. market, Omeros informed the CHMP that it will terminate its European compassionate-use program for the drug. The company confirmed that European TA-TMA patients currently receiving compassionate-use YARTEMLEA will be provided with sufficient supply to complete their treatment courses.

Looking ahead, Omeros continues to advance its MASP-2 franchise. Clinical studies evaluating the therapy for acute respiratory distress syndrome (ARDS) and the prevention of high-risk TA-TMA in pediatric patients are slated to begin later this year.

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