Discrepancies between morphologic, cytochemical, and immunologic characteristics in acute myeloblastic leukemia.

This study was designed to compare the cytochemical pattern with the immunologic phenotype in 108 cases of acute myeloblastic leukemia (AML) classified according to the French-American-British (FAB) criteria. Special attention was paid to the cases where discrepancy existed between these approaches and to a group of 11 patients considered as unclassifiable mainly because a second cell population--megakaryoblastic--was detected. Three types of discrepancies were observed: cases with typical morphologic characteristics and cytochemistry but devoid of lineage-specific antigens; these mainly include poorly differentiated leukemias (eight M1, four M2, and eight M5a), suggesting that the cytochemical enzymes are earlier myeloid markers than the currently available monoclonal antibodies; cases in which immunologic characteristics were discordant with morphologic characteristics and cytochemistry; these include two M2 cases positive for monocytic monoclonal antibodies (CD14); six M5b cases positive for granulocytic monoclonal antibodies (CD15); and seven M4 cases lacking in CD14 or CD15 antigens; cases with discrepancies between morphologic characteristics and cytochemistry and in which the immunologic markers permitted the correct assessment of cell lineage (six cases). These results show that the classification of these patients is better achieved by a combined morphologic, cytochemical, and immunologic approach.

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.

The nature of blast cells in myelodysplastic syndromes evolving to acute leukaemia.

The blast cells from nine patients with an overt acute leukaemia following a previous myelodysplastic syndrome (MDS) are analyzed with a panel of monoclonal antibodies as well as by morphological and cytochemical criteria. By integrating the results obtained with these three approaches the leukaemia in 6 patients was assessed as myeloid-granulocytic and/or monocytic-, in two as mixed- megakaryoblastic/myeloid- and in one as lymphoid. A good correlation between morphology, cytochemistry and immunological markers was observed in 7 out of the 9 cases. In three cases a noteworthy percentage of J5+ cells was detected. The exceptional finding of lymphoid as well as megakaryocytic and myeloid transformations suggests that the target cell for these leukaemias could be a pluripotent stem cell.

TdT activity in acute myeloid leukemias defined by monoclonal antibodies.

Blast cells from eight out of 71 patients diagnosed with acute myeloid leukemia (AML) by morphological, cytochemical, and immunological criteria showed TdT activity. Their distribution according to the FAB classification was one M1, one M2, one M4, two M5a, one M5b, one M6, and one undifferentiated case. The TdT+ AML cases did not show major clinical and hematological differences when compared with the classical TdT- AML patients. Other phenotypical aberrations in the expression of membrane antigens, apart from the presence of nuclear TdT, were not observed in these TdT+ cases after study with a large panel of monoclonal antibodies. A higher incidence of TdT+ cases was found among the monocytic variants of AML (M4 and M5)--four cases--than in the granulocytic variants (M1, M2, and M3)--2 cases. These TdT+ cases should be distinguished from mixed leukemias by double labeling techniques, assessing in the TdT+ AML the coexpression of TdT and myeloid markers in individual cells as shown in four of our cases.