The leukemias are cancers of the WBCs involving bone marrow, circulating WBCs, and organs such as the spleen and lymph nodes.
Risk of developing leukemia is increased in patients with
Malignant transformation usually occurs at the pluripotent stem cell level, although it sometimes involves a committed stem cell with more limited capacity for differentiation. Abnormal proliferation, clonal expansion, and diminished apoptosis (programmed cell death) lead to replacement of normal blood elements with malignant cells.
Manifestations of leukemia are due to suppression of normal blood cell formation and organ infiltration by leukemic cells. Inhibitory factors produced by leukemic cells and replacement of marrow space may suppress normal hematopoiesis, with ensuing anemia, thrombocytopenia, and granulocytopenia. Organ infiltration results in enlargement of the liver, spleen, and lymph nodes, and occasional kidney and gonadal involvement. Meningeal infiltration results in clinical features associated with increasing intracranial pressure (eg, cranial nerve palsies).
Leukemias were originally termed acute or chronic based on life expectancy but now are classified according to cellular maturity.
Acute leukemias consist of predominantly immature, poorly differentiated cells (usually blast forms). Acute leukemias are divided into lymphocytic (ALL) and myelocytic (AML) types, which may be further subdivided by the French-American-British (FAB) classification (see Table 1: Leukemias: French-American-British (FAB) Classification of Acute Leukemias).
Chronic leukemias have more mature cells than do acute leukemias. Chronic leukemias are described as lymphocytic (CLL) or myelocytic (CML—see Table 2: Leukemias: Findings at Diagnosis in the Most Common Leukemias).
Myelodysplastic syndromes involve progressive bone marrow failure but with an insufficient proportion of blast cells (< 30%) for making a definite diagnosis of AML; 40 to 60% of cases evolve into AML.
A leukemoid reaction is marked granulocytic leukocytosis (ie, WBC > 30,000/μL) produced by normal bone marrow in response to systemic infection or cancer. Although not a neoplastic disorder, a leukemoid reaction with a very high WBC count may require testing to distinguish it from CML (see Leukemias: Chronic Myelocytic Leukemia (CML)).
Last full review/revision July 2012 by Michael E. Rytting
Content last modified July 2012