Ayvakit from Blueprint Medicines Corp. was initially FDA-indicated to treat adults with unresectable or metastatic GIST harboring a platelet-derived growth factor receptor alpha (PDGFRA) exon 18 mutation, including PDGFRA D842V mutations. In June, the drug won expanded use to include advanced systemic mastocytosis based on data from the single-arm, open-label EXPLORER and PATHFINDER clinical studies.…