The drug imatinib, a selective inhibitor of Kit, improved the prognosis of GIST patients and the median overall survival is now estimated more than 5 years.23, 24, 25 However, resistance to the drug appears with prolonged use and has become a serious problem.23, 24 Most imatinib-resistant cases have a secondary Kit mutation in the kinase domain, and then lose sensitivity to the drug.24, 26, 27 Further understanding of oncogenic signals is required for establishment of effective targeting of therapy. This evidence concerns the gene KIT and gastrointestinal stromal tumor.