The subsequent years were characterized by the development of several targeted therapies such as imatinib, a small molecule inhibitor of the BCR-ABL tyrosine kinase, in chronic myeloid leukemia (CML), and gefitinib, a small molecule inhibitor of epidermal growth factor receptor (EGFR), in non-small cell lung cancer (NSCLC). This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.