PDGFRA and gastrointestinal stromal tumor: The first study that showed the correlation between the response to imatinib at a dose of 400 mg/day and mutational status in GIST was performed by Heinrich et al. One hundred and twenty-seven patients with metastatic GIST received imatinib, 71 had a tumor with a mutation of KIT exon 11, 23 of KIT exon 9, two of KIT exon 13 and KIT exon 17; PDGFRA exon 18 was mutated in six cases and nine tumors were WT.