Imatinib (mesylate) is a first generation tyrosine kinase inhibitor that is used in the treatment of chronic myelogenous leukemia (CML), gastrointestinal stromal tumors (GIST), and other cancers. It selectively targets certain tyrosine kinases, including c-ABL, platelet-derived growth factor receptor, and KIT. In CML, imatinib (mesylate) inhibits the oncoprotein BCR-ABL, the product of the Philadelphia chromosome gene fusion.