Leukemia (British English: leukaemia) (Greek leukos e , "white"; aima a µa, "blood") is a cancer of the blood or bone marrow and is characterized by an abnormal proliferation (production by multiplication) of blood cells, usually white blood cells (leukocytes). Leukemia is a broad term covering a spectrum of diseases. In turn, it is part of the even broader group of diseases called hematological neoplasms. Leukemia is clinically and pathologically subdivided into several large groups.