Leukemia or leukaemia meaning white blood (Greek leukos, "white"; aima, "blood") is a cancer of the blood or bone marrow and is characterized by an abnormal growth of blood cells, usually white blood cells (leukocytes)and is split into its acute and chronic forms. It can affect the digestive tract, kidneys, lungs, or other parts of the body and can also collect in the testicles causing swelling. Leukemia is one of the most common cancers of children, But isn't just a children's disease, as many think. It is newly diagnosed in about 29,000 adults and 2000 children each year in the United States and has four main types and many sub-types of which only some of them are common among children. Leukemia that has spread to the brain may produce central nervous system effects, such as headaches, seizures, weakness, blurred vision, balance difficulties, or vomiting and the disease, or the chemotherapy used to treat it, can cause anemia.