Usefulness of Flow Cytometry Monocyte Partitioning in the Diagnosis of Chronic Myelomonocytic Leukemia in a...

Based on CD14/CD16 expression, monocytes can be divided into the following three functionally distinct subsets: classical (MO1, CD14++/CD16-), intermediate (MO2, CD14+/CD16+) and non-classical (MO3, CD14^dim/CD16-). An expanded MO1 subset (cutoff, ≥94%) was found to be predictive of CMML. However, the utility of this test in routine practice has important limitations, with some reporting low sensitivity or a lack of correlation. Here, we sought to evaluate the practical usefulness of this test by using our routine antibody panel and a new gating strategy.

Our study included 56 peripheral blood (PB) and 69 bone marrow (BM) samples. The PB cohort included 20 patients with CMML, 21 with no myeloid neoplasms (non-MN) and 15 with other myeloid neoplasms (non-CMML-MN). The BM cohort included 25 CMML, 16 non-MN and 28 non-CMML-MN cases. Taking advantage of an existing 8-color myelomonocytic tube routinely used in our lab, we conducted a retrospective monocyte subset analysis using a new sequential gating strategy.

The assay was able to distinguish CMML from non-CMML cases with high sensitivity (90.0%) and specificity (88.9%) in blood samples using a cutoff value of MO1 > 94%. For BM samples, a reduced MO3 < 1.24% was more closely associated with CMML with a sensitivity of 96.0% and a specificity of 79.5%. A side-by-side comparison of our assay with the original "monocyte assay" showed strong agreement.

Our study demonstrates the utility of a practical and robust approach for monocyte subset analysis in the diagnosis of CMML.