KIT and gastrointestinal stromal tumor: In a previous study, 74% of GISTs analyzed had at least one nondriver genetic abnormality.164 In that report, the most frequently mutated genes were TP53, RB1, SETD2, PTEN, MAX, PIK3CA, and TSC1, and the most prevalent copy number alteration in KIT-mutated GIST was CDKN2A deletion.164 In addition, activation of alternate receptor tyrosine kinases has been suggested as a mechanism of resistance to currently approved TKIs.