Europe confirms its refusal of narsoplimab, leaving children with TA-TMA on opposite sides of the Atlantic
The EMA has upheld its negative opinion on Omeros’s Yartemlea for transplant-associated thrombotic microangiopathy in adults and children from two years of age. The FDA approved the same drug for the same population in December 2025.
In brief
The EMA confirmed its refusal of Yartemlea (narsoplimab) for TA-TMA after re-examination, citing uncontrolled data and too little evidence in children.
- The CHMP confirmed its refusal of Yartemlea on re-examination on 15 October 2026, after a first negative opinion on 25 June.
- The main study was a single-arm trial in 28 adults; the children’s data came from an expanded access programme that included 16 children.
- Omeros says it will end the EU compassionate use programme, citing demand in the US, where the drug has been approved since December 2025.
The European Medicines Agency has confirmed its refusal to authorise Yartemlea (narsoplimab), Omeros’s antibody for haematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA). The CHMP adopted its final negative opinion on 15 October 2026 after a re-examination requested by the company, and the agency published the outcome the following day.
The intended indication covered adults and children from two years of age. That is the population for which the FDA approved the drug in December 2025, according to Omeros, making narsoplimab another case in which US and European regulators have reached different conclusions on the same evidence.
The evidence package
The main study gave Yartemlea to 28 adults with thrombotic microangiopathy after a stem cell transplant. It had no placebo or active comparator, and its primary measures were changes in platelet counts and lactate dehydrogenase. Supporting data came from an expanded access programme in 27 adults and 16 children, and from a comparison of survival with similar patients who did not receive the drug.
The EMA said the company had not provided sufficient evidence of effectiveness. It pointed to the lack of a control group, concomitant medicines, changes made during the study, and how effectiveness was measured and the dose chosen. Published literature showed similar results with other treatments, and the survival comparisons could not reliably confirm the drug’s effect. The company also explored a conditional marketing authorisation, but the agency concluded the criteria were not met because benefit had not been demonstrated.
The paediatric question
On children, the agency was blunt. There were not enough data to support the proposed dose or to assess effectiveness and safety, and because benefit had not been shown in adults, the results could not be reliably extended to younger patients.
Extrapolation to children only works when there is something established in adults to extrapolate from.
That logic will be familiar to sponsors of rare disease programmes, where adult single-arm data are often the anchor for a paediatric indication. When the adult anchor fails, the paediatric case usually fails with it.
The company’s response
Omeros said the re-examination process was flawed. It noted that an ad hoc expert group had recommended review of individual patient-level data by external experts, and that the CHMP did not provide those data to the group. “We are deeply disappointed in the re-examination process and outcome,” said Gregory Demopulos, chairman and chief executive.
The practical consequences extend beyond the refusal. Omeros has told the agency it will end its EU compassionate use programme because of rising demand in the US commercial market, although patients currently being treated will receive enough drug to complete their courses. The company says it is working on named-patient access where permitted, and plans a study of narsoplimab for prevention of high-risk TA-TMA in paediatric patients.
