Progressive, malignant disease of the blood-forming organs, characterized by distorted proliferation and development of leukocytes and their precursors in the blood and bone marrow; classified according to degree of cell differentiation as acute or chronic, and according to predominant type of cell involved as myelogenous or lymphocytic.

Leukemia (also spelled leukaemia; pronounced loo-KEE-mee-ə) is a group of blood cancers that usually begin in the bone marrow and produce high numbers of abnormal blood cells. These blood cells are not fully developed and are called blasts or leukemia cells...