(= leukemia (USA) )Malignant neoplasia of leucocytes. Several different types are recognized according to the stem cell that has been affected, and several virus-induced leukaemias are known (eg. that caused by feline leukaemia virus). Both acute and chronic forms occur: (1) Acute lymphoblastic leukaemia (ALL) - neoplastic proliferation of white cell precursors in which the blood has large numbers of primitive lymphocytes (high nuclear/cytoplasmic ratio characteristic of dividing cells and few specific surface antigens expressed) ; tends to be common in the young;(2) Acute myeloblastic leukaemia (AML) - more common in adults; the proliferating cells are of the myeloid haematopoietic series and the cells appearing in the blood are primitive granulocytes or monocytes;(3) Chronic lymphocytic leukaemia (CLL) - neoplastic disease of middle or old age, characterized by excessive numbers of circulating lymphocytes of normal, mature appearance, usually B-lymphocytes; presumably a neoplastic transformation of lymphoid stem cells;
Dictionary of molecular biology. 2004.