Leukemia is a cancer of the white blood cells that develops in the bone marrow and causes uncontrolled increase in leukocytes. It has no known single cause but genetic, environmental, and immunodeficiency factors are believed to play a role. Leukemia affects the bone marrow and leukocytes. Symptoms vary but can include fever and infection. Treatment may involve chemotherapy, radiotherapy, bone marrow transplant, or antibiotics. Prevention is not possible as the cause is unknown.