EMA confirms refusal of Omeros' narsoplimab after re-examination in transplant TMA

The European Medicines Agency confirmed on 15 October 2026 that it recommends refusing a marketing authorisation for Yartemlea (narsoplimab), Omeros Ireland Limited's antibody for thrombotic microangiopathy after haematopoietic stem cell transplant (HSCT). The re-examination upheld the negative opinion the agency first issued on 25 June 2026 ¹.

What the agency assessed

Narsoplimab is a monoclonal antibody that binds MASP-2, a protein in the complement system, and was to be given by intravenous infusion to adults and to children from two years of age with high-risk disease. It has held EU orphan designation since 22 November 2018 ¹.

The core of the application was a single study of 28 adults who all received Yartemlea, with no placebo or comparator arm. Its main efficacy measure was the change in platelet and lactate dehydrogenase levels, used as markers of the disease, alongside organ function and the need for transfusions. Omeros added data from 27 adults and 16 children treated through an expanded access programme, and a comparison of survival against similar patients who did not receive the drug ¹.

The EMA found that evidence insufficient. Patients in the main study were also taking other medicines, so the agency could not tell whether any benefit came from Yartemlea, from those medicines or from something else. It also raised concerns about changes made during the study, how effectiveness was measured and how the dose was chosen. Published studies showed other treatments for the condition giving similar results, and the survival comparison against untreated patients could not reliably confirm an effect. For children, the agency said there were too few data to back the proposed dose, and adult results could not be extended to them because benefit in adults had not been shown ¹.

During re-examination the EMA reassessed the data, consulted a group of experts in HSCT and its complications, and took in views from other clinicians who contacted it. It concluded that the original concerns were still unresolved ¹.

What it means for the market

The decision is a clear statement of where the EMA draws the line on single-arm evidence in a rare, life-threatening condition. Omeros considered switching to a conditional marketing authorisation, the route meant for unmet needs where less complete data can be accepted. The agency rejected that too, on the grounds that the criteria for a conditional authorisation were not met because the medicine's benefits are not demonstrated ¹. For developers planning EU filings built on uncontrolled studies, external comparisons or expanded access data, the ruling shows that orphan status and a serious unmet need do not lower the bar for showing that the drug itself caused the effect.

The outcome also splits the drug's position across the Atlantic. Yartemlea is authorised in the United States, and Omeros told the EMA that rising US demand is behind its plan to end the EU compassionate use programme. Patients already on treatment will receive enough medicine to finish their courses ¹. Clinicians in Europe treating new patients with this complication lose that access route ¹.

The EMA's text does not say whether Omeros will run a controlled study or file again in the EU, and gives no estimate of the number of European patients affected ¹.

Caveats

The opinion rests on one small uncontrolled study of 28 adults plus expanded access data, so the EMA's finding is that benefit was not demonstrated, not that the drug was shown not to work ¹. The company is assessing all ongoing clinical trials required for authorisation in the European Union ¹.