Chronic myeloid leukemia is a disease caused by a genetic mutation that gives rise to this abnormal protein molecule. The abnormal protein triggers the bone marrow to release dangerous numbers" of white blood cells. Gleevec, the thin molecule shown here in blue, has a specific shape which blocks the active site of the abnormal protein. By binding to the active site, Gleevec prevents the trigger protein from causing the release the white blood cells and alleviates the symptoms of the disease.