Imatinib mesylate is indicated in the treatment of patients with chronic myeloid leukemia (CML) in blast crisis, the accelerated phase of disease, or in the chronic phase of disease after not responding to interferon-alpha therapy. Studies are being conducted to evaluate the drug in treating gastrointestinal (GI) stromal tumors (GIST, a form of sarcoma), small-cell lung cancer, prostate cancer, and glioblastoma.