THE DIAGNOSTIC AND PROGNOSTIC VALUE OF IMMUNOPHENOTYPING IN ACUTE-LEUKEMIA

Immunophenotyping with monoclonal antibodies to leucocyte differentiat ion antigens has an established diagnostic role in the laboratory inve stigation of acute leukemia. In the vast majority of cases, a hemopoie tic lineage can be confidently assigned; namely, acute myeloid leukemi a (AML), or the precursor-B and precursor-T variants of acute lymphobl astic leukemia (ALL). The areas of greatest practical importance are i n morphologically difficult or undifferentiated cases, and in distingu ishing between the major variants of precursor-B and T-ALL. Cases with aberrant patterns of marker expression (acute mixed lineage leukemia, lineage infidelity) are frequently encountered in both ALL and AML, a nd can lead to diagnostic confusion. However, correlation with morphol ogy and other clinicopathologic features, and careful consideration of the weight of phenotyping evidence almost always allows the correct l ineage to be identified. The prognostic value of phenotypic informatio n in acute leukemia is generally limited. Recognition of the major var iants of ALL is still of clinical importance, but the significance of myeloid antigen positivity in ALL is controversial, and may not have p rognostic value. Patterns of myeloid antigen expression in AML have li mited prognostic significance, while the relationship between lymphoid antigen expression and treatment response in AML remains highly contr oversial. Careful evaluation of the predictive power of immunophenotyp e in large controlled clinical trials in acute leukemia is still requi red.