Significance of lineage specific differentiation markers for complex classification of acute leukemias. II. Acute lymphoblastic leukemias.

Acute lymphoblastic leukemias originate from cells committed either to the T-lineage (T-ALL) or B-lineage (nonT-ALL). Leukemic cells are allocated to these lineages according to the expression of lineage specific differentiation markers (LSDM), which are T-cell antigen receptors for the T-cell lineage and immunoglobulins for the B-cell lineage. T-ALL seem to be one type of disease, among nonT-ALL it is possible to distinguish several types of diseases according to the immunoglobulin expression and clinical findings. The specificity of monoclonal antibodies and other markers is discussed with regard to the classification of ALL and "hybrid acute leukemias" (hAL), the latter with cells differentiating into myeloid and lymphoid lineages. The existence of a single hAL has not yet been reliably proved with the use of LSDM. Short-term cultures of leukemic cells represent useful diagnostic tools particularly for acute unclassifiable leukemias. Present knowledge of karyotype findings in acute leukemias classified according to LSDM is reviewed and the necessity to introduce a complex classification on this basis stressed.