Omeros hits endpoint in pivotal stem cell transplant study

Seattle, where Omeros is based (Pixabay)

A pivotal trial of Omeros’ narsoplimab in hematopoietic stem cell transplant (HSCT) patients has hit its primary endpoint. Omeros expects to use the data to win FDA approval, although secrecy around the design of the trial means there remains scope for skepticism about the results.

Narsoplimab, also known as OMS721, is an anti-MASP-2 antibody that Omeros thinks can counter the complement activation thought to play a role in HSCT-associated thrombotic microangiopathy, a potentially fatal complication of using stem cells to treat hematological malignancies. In an earlier trial, Omeros classed a little more than half of 19 patients treated with narsoplimab as responders.

The pivotal single-arm trial matched that performance, with 56% of patients achieving the full set of response criteria. After 100 days, 65% of the patients were alive. A HSCT physician quoted by Omeros said the typical 100-day survival rate is less than 20%.


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Omeros has provided the data to the FDA, furthering a rolling submission that it expects to complete in the first half of next year. However, while Omeros and the FDA know what happened in the trial, everyone else is in the dark about some key points.

Specifically, Omeros is yet to reveal the number of patients in the trial or the criteria participants had to meet to be classed as responders. Omeros said it is keeping that key information confidential for “competitive business reasons.” In July, Omeros said it had reached agreement with the FDA on the response criteria used in the primary endpoint.

Narsoplimab has stumbled in other indications. Last year, the drug performed no better than placebo at reducing proteinuria in patients with IgA nephropathy. Omeros moved into the IgA nephropathy phase 2 trial on the strength of encouraging data in the indication in four patients.

Shares in Omeros rose around 9% in premarket trading following the release of the results. 

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