Omeros Corporation (NASDAQ:OMER) shares declined 4% in Friday morning trading after the European Medicines Agency’s (EMA) Committee for Medicinal Products for Human Use (CHMP) maintained its negative opinion on the company’s marketing authorisation application for narsoplimab.
The decision followed a formal re-examination of the application for narsoplimab as a treatment for haematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), a serious complication that can develop following stem cell transplantation.
The CHMP reaffirmed its original negative opinion issued in June 2026, representing a further regulatory setback for the treatment in Europe.
The outcome contrasts with the drug’s regulatory position in the United States, where narsoplimab received approval from the Food and Drug Administration (FDA) in December 2025 under the brand name YARTEMLEA.
CHMP Maintains Negative Opinion Following Re-examination
The CHMP confirmed its negative assessment of narsoplimab following a formal review requested after its initial decision in June.
The application sought European marketing authorisation for the treatment of TA-TMA, a condition involving damage to small blood vessels that can result in serious complications following haematopoietic stem cell transplantation.
The committee’s latest opinion means that the application has not received a positive recommendation for European approval.
The re-examination involved consideration of the clinical evidence supporting narsoplimab, including patient-level information submitted by Omeros.
However, the committee maintained its previous position despite the additional review process.
The decision creates uncertainty over the company’s ability to obtain European marketing authorisation for narsoplimab under the current application.
Expert Group Recommended Further Patient-Level Data Review
As part of the re-examination, the CHMP convened an eight-member ad hoc expert group.
The panel included haematologists, statisticians, transplant physicians and patient representatives.
According to the CHMP’s final meeting minutes, the group recommended that external specialists examine individual patient-level data to gain a clearer understanding of factors influencing treatment response and survival.
The recommendation reflected the importance of assessing outcomes among patients with TA-TMA, particularly where differences in clinical characteristics may affect treatment results.
Omeros had submitted substantial patient-level data to the CHMP in August 2026.
However, according to the account provided, the committee did not make that information available to the expert group before reaching its final decision.
The reported handling of the data has become a point of contention in the regulatory process.
The CHMP nevertheless maintained its negative opinion following the re-examination.
Narsoplimab Approved in United States Under YARTEMLEA Brand
The European decision differs from the regulatory outcome in the United States, where the FDA approved narsoplimab in December 2025.
The treatment is marketed under the brand name YARTEMLEA and is authorised for patients aged two years and older with TA-TMA.
According to Omeros, YARTEMLEA is the first and only FDA-approved treatment specifically indicated for the condition.
The drug targets MASP-2, an enzyme involved in the lectin pathway of the complement system.
The complement system forms part of the body’s immune response, while the lectin pathway contributes to immune activation.
By inhibiting MASP-2, narsoplimab is designed to interfere with this pathway.
Omeros also highlights the treatment’s US regulatory safety profile, stating that it is the only marketed systemic complement inhibitor that does not require a boxed warning, a Risk Evaluation and Mitigation Strategy (REMS), or specific vaccinations.
These distinctions relate to the drug’s approved US labelling and regulatory requirements and do not change the CHMP’s assessment of the European application.
Omeros to End European Compassionate-Use Programme
Following the regulatory outcome, Omeros informed the CHMP that it intends to terminate its European compassionate-use programme for YARTEMLEA.
The company cited increasing commercial demand for the treatment in the United States as a factor behind the decision.
Compassionate-use programmes can provide access to medicines for patients with serious conditions when authorised treatment options are limited or unavailable.
Omeros confirmed that European patients currently receiving YARTEMLEA through the programme will be supplied with sufficient medication to complete their existing treatment courses.
The company did not disclose how many patients are currently receiving treatment under the European programme.
It also did not provide a detailed timetable for ending access for new patients.
The decision will affect the availability of narsoplimab through the company’s compassionate-use arrangements in Europe while the treatment remains commercially available in the United States.
Omeros Continues Development of MASP-2 Treatments
Despite the European regulatory setback, Omeros is continuing to develop additional clinical applications for its MASP-2-targeting technology.
The company plans to begin clinical studies later in 2026 evaluating the therapy in acute respiratory distress syndrome (ARDS).
ARDS is a serious respiratory condition involving inflammation and fluid accumulation in the lungs, which can significantly impair oxygen exchange.
Omeros is also preparing studies investigating the prevention of high-risk TA-TMA in paediatric patients.
These programmes would explore potential uses of MASP-2 inhibition beyond the treatment’s existing US indication.
However, the proposed studies remain subject to clinical development risks, and successful results would be required to support any future regulatory submissions.
The company has not provided detailed trial designs, enrolment targets or expected completion dates in the announcement.
Investors Assess European Setback and US Commercial Prospects
The CHMP’s decision represents a further obstacle to European approval for narsoplimab following the original negative opinion in June 2026.
The outcome also raises questions about the company’s future regulatory strategy in Europe, particularly following the reported disagreement over the review of patient-level clinical data.
In the United States, YARTEMLEA remains FDA-approved for TA-TMA in patients aged two years and older, providing Omeros with an established regulatory pathway for commercial sales.
The company has cited increasing US demand for the treatment, although the announcement did not provide updated revenue or prescription figures.
Omeros shares declined 4% following the European decision, reflecting the market’s response to the regulatory setback.
Investors will continue to monitor US commercial uptake, any further developments involving European regulators and progress in the company’s planned ARDS and paediatric TA-TMA studies.