Prognostic value of immunophenotypic characteristics of blast cells in acute myeloid leukemia

In order to elucidate the prognostic role of cytofluorimetry analysis of leukemic cells in AML, the immunophenotypic characteristics of blast cells obtained from 66 AML patients belonging to M0-M2 and M4-M5 FAB subtypes have been investigated by flow cytometry using a large panel of monoclonal antibodies (McAbs) utilized in single, double, and triple fluorescence experiments. On a univariate analysis, four different immunophenotypic blast cell characteristics were found to be associated with a poor prognosis: expression of CD34 "bright" (ratio > 10 between fluorescence emission of positive cells and that of negative (isotypic) control-P/N ratio: mean MESF value: 265,000) in > 15% blast cells, co-expression of CD34 and CD33 in > 60% blast cells, expression of CD14 in > 30% leukemic cells, the MDR+ ("multiple drug resistant") phenotype. In contrast, the duration of remission, and overall survival of AML patients showing a "dim" CD34 expression (P/N ratio: 3-10: mean MESF value: 49,000) was similar to that of CD34- AML patients, irrespective of the percentage of positivity for CD34, which was, however, a predictive factor of survival in patients with higher CD34 fluorescence intensities in their blastic population. No correlation between FAB subtypes, prognosis and immunophenotype was found. The multivariate regression analysis showed that, besides age, only the combined expression of CD34 and CD33 had independent prognostic meaning. Indeed, in each FAB subtypes the CD34+/CD33+ phenotype was associated with a shorter survival and a lower mitotic rate. These data may contribute to the understanding of the discrepancies so far observed in the literature regarding the prognostic role played by the CD34 expression on leukemic AML blasts.