Leukemia (American English) or leukaemia (British English) (from the Greek leukos λεύκος - white, and haima αίμα - blood) is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called "blasts". Leukemia is a broad term covering a spectrum of diseases. In turn, it is part of the even broader group of diseases affecting the blood, bone marrow, heart, and lymphoid system, which are all known as hematological neoplasms. Leukemia can also cause multiple organ failure.
In 2000, approximately 256,000 children and adults around the world developed some form of leukemia, and 209,000 died from it.