All tumors from the three PDX models had both primary and secondary KIT mutations, which explains their resistance to TKIs, i.e., KIT exon 11 (p.Y570_L576del) and KIT exon 17 (p.D816E) mutations in GIST-RX1, KIT exon 11 (p.K550_splice) and KIT exon 14 (p.T670I) mutations in GIST-RX2, and KIT exon 9 (p.502_503insYA) and KIT exon 17 (p.D820E) mutations in GIST-RX4. This evidence concerns the gene KIT and gastrointestinal stromal tumor.