Tumor markers found in blood, urine and body tissues can be used in diagnosing and treating cancer. Each tumor marker is indicative of a particular disease and thus can be used for the screening, monitoring and diagnosis of specific tumor types. In addition to being used in prognosis, these molecular markers help to predict the response, resistance and toxicity to therapy. For example, BCR-ABL gene sequence detection is used to diagnose chronic myelogenous leukemia and acute lymphatic leukemia.