Leukemia is a cancer that affects the blood and bone marrow. It causes the body to overproduce immature white blood cells that do not function properly. There are four main types of leukemia - acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), acute myelogenous leukemia (AML), and chronic myelogenous leukemia (CML). The document discusses the definition, causes, signs and symptoms, diagnosis, treatment approaches which may include chemotherapy, targeted therapy and stem cell transplant, and management of the different types of leukemia.