** Biotech firm Omeros' OMER.O shares fall 25.2% to $8.02 premarket

** Company says European Medicines Agency's key panel issued a negative opinion on its application for its drug narsoplimab to treat transplant-associated thrombotic microangiopathy (TA-TMA)

** TA-TMA is a severe and often fatal complication that can occur after stem cell transplant in adults and children

** OMER to request a re-examination of the opinion and review by an independent expert group

** The drug, branded as Yartemlea in the United States, received approval by the U.S. FDA in December 2025 for TA-TMA patients aged two years and older

** As of last close, OMER down 37.6% YTD