An observational study evaluated the clinical and molecular features of KIT/PDGFRA WT-GISTs in a cohort (patients < 19 y with GIST or > 19 y with WT-GIST), which was characterized by IHC for SDHB, sequencing of SDH genes, determination of SDHC promoter methylation, as well as germline testing of SDH genes for some of them (consented). The gene discussed is PDGFRA; the disease is gastrointestinal stromal tumor.