Cancer is a disease where abnormal cells divide uncontrollably and spread to other tissues. There are over 100 types of cancers. Leukemia is a cancer of the blood cells that starts in the bone marrow. The main types of leukemia are acute lymphocytic, acute myelocytic, chronic lymphocytic, and chronic myelocytic. Symptoms of leukemia include infections, anemia, bruising, weight loss, sweats, and bone pain. Risk factors include radiation, smoking, benzene exposure, chemotherapy, and family history. Diagnosis involves medical exams, blood tests, biopsies, and scans to determine the type and extent of the cancer.