Omeros stock plunges after EMA rejects narsoplimab

Omeros Corp. shares dropped sharply after a European Medicines Agency expert panel issued a negative opinion on the company’s marketing application for narsoplimab (Yartemlea) to treat hematopoietic stem cell transplant–associated thrombotic microangiopathy (TA‑TMA) in Europe. Omeros plans to request a re‑examination through the EMA’s Ad Hoc Expert Group and to appeal the decision.

The EMA committee cited shortcomings in the clinical data package. The primary study enrolled 28 adults and did not include a randomized, placebo‑controlled comparator arm. The panel concluded that the limited, uncontrolled data did not provide sufficient evidence of absolute efficacy to support a marketing authorization for TA‑TMA in the European Union.

The opinion was released on a Friday as U.S. trading began, triggering heavy selling of OMER shares. The stock has fallen about 50% since the start of 2026. Management notified investors of its intent to pursue the EMA re‑examination process.

Analysts adjusted forecasts after the panel’s decision, lowering ex‑U.S. revenue projections for 2026 and 2027 to reflect the delay or potential loss of revenue from a European launch that had been expected in mid‑2026. Appeals under the EMA framework can take several months, and reversals of initial negative opinions are uncommon.

Domestic commercial performance remains measurable. Yartemlea generated $9.9 million in net sales in the first quarter of 2026, above the Wall Street consensus of $4.1 million. The U.S. Centers for Medicare & Medicaid Services finalized a permanent, product‑specific reimbursement J‑code (J1289) for Yartemlea, effective July 1, 2026; the J‑code will be used for institutional billing and reimbursement.

Narsoplimab is a monoclonal antibody developed for TA‑TMA, a severe vascular complication that can follow bone marrow or stem cell transplantation. Omeros will seek a formal re‑examination by an Ad Hoc Expert Group at the EMA and continue its regulatory and commercial work in the U.S. while the European appeal proceeds.