Acute monoblastic/monocytic leukemia and chronic myelomonocytic leukemia share common immunophenotypic features but differ in the extent of aberrantly expressed antigens and amount of granulocytic cells.

Differentiation between acute monoblastic/monocytic leukemia (AMoL) and chronic myelomonocytic leukemia (CMML) can be difficult. Therefore, we compared immunophenotypes between 27 cases of AMoL and 138 cases of CMML. Monocytopoietic cells showed aberrant coexpression of CD56 in all cases of AMoL vs. 81.9% of CMML (p = 0.015). No other aberrantly expressed antigen was found in AMoL, while in CMML CD2 coexpression was found in 21.7% (p = 0.005), lack of CD13 in 10.9%, and of HLA-DR in 4.3% (NS). Cytomorphology identified higher blast percentages and lower percentages of monocytes and granulocytic cells in AMoL (p <0.001). Multiparameter flow-cytometry (MFC) found higher percentages of blasts (17.6 ± 25.2 vs. 4.1 ± 3.2, p <0.001) and monocytopoietic cells (29.1 ± 27.5 vs. 19.9 ± 12.2, p = 0.012) in AMoL and more granulocytic cells in CMML (52.4 ± 19.2 vs. 26.0 ± 22.4, p <0.001). The mean ratio of monocytic:granulocytic cells was higher in AMoL (5.0 vs. 0.8; p <0.001). It can be concluded that AMoL and CMML differ in aberrantly expressed antigens and the amount of granulocytic cells.