- A drug used to treat certain types of leukemia and other blood cancers, gastrointestinal stromal tumors, skin tumors called dermatofibrosarcoma protuberans, and a rare condition called systemic mastocytosis. It is also being studied in the treatment of other conditions and types of cancer. Imatinib mesylate blocks certain proteins made by the BCR-ABL, PDGFR, or c-KIT oncogene, which may help keep cancer cells from growing and may kill them. Imatinib mesylate is a type of tyrosine kinase inhibitor. Also called Gleevec and STI571.