To understand TKI resistance mechanisms, a panel of four representative leukemia cell lines with activating mutations, BCR/ABL (K562, KU812), KIT (Kasumi-1) and FLT3 (MV4-11), rendering them sensitive to kinase-targeted therapies were initially exposed to increasing concentrations of representative TKIs, nilotinib, imatinib, or PKC412, until they could grow in medium containing 1 μM of the respective drug. The gene discussed is KIT; the disease is leukemia.