P1027: RESPONSES TO AVAPRITINIB IN PATIENTS WITH ADVANCED SYSTEMIC MASTOCYTOSIS: HISTOPATHOLOGIC ANALYSES FROM EXPLORER AND PATHFINDER CLINICAL STUDIES. (23rd June 2022) - George, T.; Karner, K. H.; Moser, K. A.; Rets, A.; Reiter, A.; Radia, D. H.; Deininger, M.; Lin, H.-M.; Dimitrijević, S.; DeAngelo, D. J.