Imatinib is a tyrosine kinase inhibitor that specifically targets the kinase activity of PDGFRβ, ABL, and c-KIT and has been approved for the treatment of chronic myeloid leukemia and gastrointestinal stromal tumors (20, –, 24). The gene discussed is PDGFRB; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.