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The classification of leukaemia 

The classification of leukaemia

The classification of leukaemia

Wendy N. Erber


July 30, 2015: This chapter has been re-evaluated and remains up-to-date. No changes have been necessary.

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date: 30 March 2017

Leukaemia is a malignant neoplasm of haematopoietic cells originating in the marrow and spreading to the blood and other tissues, such as the lymph nodes, spleen, and liver. The characteristic feature of the neoplastic cells is that they retain the ability to proliferate but fail to differentiate normally into functional haematopoietic cells. This results in replacement of the normal bone marrow by the leukaemic cells.

General approach to classification of leukaemia

Leukaemias are subdivided into acute or chronic and lymphoid or myeloid on the basis of the cell lineage and stage of differentiation of the malignant cell. This is of fundamental importance because each subtype differs in clinical behaviour, prognosis, and response to treatment.

Clinical approach—morphological assessment of the blood film and (usually) bone marrow aspirate is essential. The cellular morphology may be diagnostic and is used to determine which ancillary tests are required for classification. Establishing the cell lineage and stage of differentiation is achieved by phenotyping the neoplastic cell using a panel of antibodies to cellular antigens associated with specific cell types (lymphoid or myeloid lineage; B-, T- or NK-cells) and degree of maturation. Determining the genotype of the malignant cell, e.g. by examination for chromosomal translocations and other genetic abnormalities, is the defining property for some acute leukaemias and can be prognostically significant.

WHO classification of acute and chronic leukaemias

The following classes of leukaemia are recognized: (1) precursor B- and T-cell neoplasms—lymphoblastic leukaemias/lymphomas; (2) acute myeloid leukaemias—including subtypes with recurrent genetic abnormalities, with myelodysplasia-related changes, therapy-related and ‘not otherwise specified’; (3) acute leukaemias of ambiguous lineage; (4) mature B-cell neoplasms—including chronic lymphocytic leukaemia; (5) mature T-cell and NK-cell neoplasms—including T-cell prolymphocytic leukaemia; (6) myeloproliferative neoplasms—including chronic myelogenous leukaemia; (7) myelodysplastic/myeloproliferative neoplasms.

This classification of leukaemia cannot be regarded as fixed and definitive—it will certainly need to be revised as new discoveries are made and new disease subtypes defined.

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