Emerging utility of flow cytometry in the diagnosis of chronic myelomonocytic leukemia

•Historically, flow cytometry has played little if any role in the diagnosis of CMML.•Monocyte subset analysis by flow cytometry is a promising ancillary test for CMML.•Monocyte subset analysis can identify CMML with high sensitivity and specificity. The diagnosis of many hematologic malignancies has shifted from being based almost exclusively on morphology and clinical data to include ancillary studies such as flow cytometry. This trend has yet to affect the diagnosis of chronic myelomonocytic leukemia (CMML) as flow cytometry, while being integral in the diagnosis of many hematologic malignancies, has no explicit role in the current WHO criteria for CMML. The absence of WHO-determined criteria for flow cytometry in the diagnosis of CMML is not due to a lack of research on the subject over the years. Herein, we review the literature concerning the use of flow cytometry in the diagnosis of CMML, focusing on recent studies showing that CMML can be differentiated from other hematologic malignancies and reactive monocytoses by the quantification of monocyte subsets by flow cytometry with high sensitivity and specificity. We also detail how this methodology could be used clinically, both as a diagnostic test and potentially as a screening test.