Gain-of-function mutations in KIT involve exon 11 (70%), exon 9 (approx 15%), exon 13 (2%), and exon 17 (1%). PDGFR mutations involve exon 18 (5%), exon 12 (1%), and exon 14 (<0.5%).

Imatinib is a competitive inhibitor for the ATP-binding domain. Imatinib binds the inactivated form of KIT and prevents conformational shift to the active form.

Primary and secondary resistance to imatinib results in a conformational shift in the kinase domain of KIT that favors the activated state.