KIT and gastrointestinal stromal tumor: Thus, the first tyrosine kinase inhibitor (TKI) that was introduced into the clinic, imatinib mesylate [30], an inhibitor of oncogenic breakpoint cluster region-abelson tyrosine protein kinase, BCR-ABL, and C-KIT, turned out to exert (part of) its activity against gastrointestinal stromal tumors (which depend on oncogenic C-KIT) by harnessing the immune system [31–33].