Imatinib is a drug that is used to treat certain types of leukemia, bone marrow disease, intestinal tumors and types of skin cancer. The same drug is used to prevent the growth of cancer cells in a patient who has gastrointestinal tumors. Imatinib also treats mastocytosis in various parts of the body. This drug works by preventing the growth of cancer cells, as it is a protein-tyrosinekinase inhibitor. Cancer cells have abnormal tyrosine kinase proteins that are responsible for telling the cell to continuously divide itself. Imatinib works by blocking the signals these abnormal proteins send, thus preventing them from multiplying further.