PDGFRA and gastrointestinal stromal tumor: PDGFRA mutations are discovered in exon 18, exon 12, exon 14, and exon 4,28involving the A-loop encoded by exon 18, JM region encoded by exon 12 or the ATP-binding domain encoded by exon 14.96Mutations in exon 18 D842V located within the kinase domain activation loop is the most common PDGFRA mutation and takes up about 65% of all PDGFRA mutations in GIST.28, 30, 40Exon 12 PDGFRA mutation is more frequently detected as a deletion than a duplication, and the most frequent site is 1821T → A, causing the V561D substitution at the protein level.