CD34+/CD33+ blast cells: correlation with FAB subtypes.

Abstract

The reproducibility of FAB morpho-cytochemical classification in a multicenter trial was recently assessed as 78.1%. The relevance of immunophenotyping in AML is debated because of the lack of a clear prognostic impact and the necessity of uniform diagnostic criteria and standardised methodologies. Several authors, studying the morpho-immunological characteristics of AML blasts by flow cytometry, suggested the necessity for the definition of clusters of cells with similar morphological patterns and intensity of expression. In this respect we reviewed blast CD34 and CD33 intensity of expression in 65 AMLs classified according to the FAB criteria. Four morphological groups could be identified: 1) low side scatter (SSC) and forward scatter (FSC); 2) intermediate SSC and FSC; 3) high SSC and FSC; 4) combination of pattern 2 plus 3. Five immunological patterns were defined: a) high CD34 expression with negative or weak CD33; b) high CD34 and CD33 expression; c) weak to negative CD34 with high CD33 expression; d) coexistence of 2 different subpopulations; e) negative to weak CD34 and CD33 expression. Based on this morpho-immunological analysis we were able to subdivide AML patients into 5 homogeneous subgroups and a comparison with FAB classification showed a concordance of 73.9%. Regarding CD34 and CD33 intensity of expression, a correlation with prognosis was demonstrated among all M1-M2 patients and in the M2 and M4 subgroups. In conclusion even if immunophenotype cannot substitute the FAB approach to AML, we feel that a flow cytometry morpho-immunological analysis could be helpful in achieving a greater understanding and agreement between different Institutions and assist in the definition of more precise prognostic subgroups.