Surface marker analysis in acute myeloid leukaemia and correlation with FAB classification.

The immunological phenotype of blast cells in 102 patients with acute myeloid leukaemia (AML) was analysed with a panel of 20 monoclonal antibodies and the enzyme terminal transferase, and correlated with the FAB classification. Although a partial correlation between these two approaches could be observed, almost every morphological group contained patients from more than one immunological phenotype. The M1 and M5a leukaemias showed the most undifferentiated phenotype, often lacking in specific myelomonocytic antigens. The M3 formed a uniform group defined as My7+, Ia-, FMC8+, a phenotype which was also observed in two cases of the microgranular variant. The granulocytic (CDw15) and monocytic (CDw14) antibodies crossreacted with some M5b and M2 leukaemias, respectively. Compared with M5a, the M5b leukaemias showed a large increase in the expression of CDw14 antigen, confirming the validity of the morphological differentiation. Glycophorin-A was present in four out of five M6 leukaemias. TdT activity was demonstrated in 10% of AML cases, with a higher incidence among the monocytic variants: M4 and M5-. Eleven AML were considered as unclassifiable according to the FAB criteria and in seven of them a megakaryoblastic cell population (GP IIb/IIIa+, GPIb+) was demonstrated; this confirms the need to include the subgroup of megakaryoblastic leukaemias within the AML. Finally, a possible immunological classification for AML is proposed.