Assessment of myeloid and monocytic dysplasia by flow cytometry in de novo AML helps define an AML with myelodysplasia-related changes category

Aims: In recent years, multiparameter flow cytometry has been increasingly recognised as an important tool in diagnosis of myelodysplastic syndrome and acute myeloid leukaemia (AML). Assessment of myeloid and monocytic 'immunophenotypic' dysplasia by flow cytometry in de novo AML has not been evaluated. Methods: 97 cases of de novo AML cases were identified and reviewed by three hematopathologists. 'Immunophenotypic' dysplasia was assessed on blasts, monocytes and granulocytes by mean fluorescence intensity. Results: Using the 2008 WHO classification criteria, there were 53 AML-not otherwise specified (NOS) (55%) and 28 AML with myelodysplasia-related changes (AML-MRC) (29%), while 16 cases were ambiguous as to AML-MRC status due to limited maturing cells for morphologic but adequate events number for immunophenotypic evaluation (AML-not evaluable, 16%). Compared with AML-NOS, granulocytic cells in AML-MRC had higher CD33 expression but lower CD45, CD11b and CD15. Monocytes in AML-MRC had lower expression of CD14, CD56 and CD45. Morphologic dysplasia was associated with significantly lower granulocytic forward scatter, side scatter and CD10 but higher CD33 expression. Conclusions: Our results suggest that the workup of AML cases should include flow cytometric assessment of granulocytes and monocytes. This analysis can aid a morphologic impression of multilineage dysplasia in distinguishing AML-MRC from AML-NOS, especially in cases with limited maturing myeloid cells.