In the last version of the WHO classification of myeloid malignancies, flow cytometry and molecular investigation are listed as potentially useful, yet non-essential diagnostic tools in hard-to-recognize chronic myelomonocytic leukemias (CMML). Flow recognition of CMML was initially based on an increase in the fraction of peripheral blood, CD14+,CD16- classical monocytes ≥94% of total monocytes. An associated inflammatory disease can preclude the detection of classical monocyte fraction increase by inducing accumulation of CD14+,CD16+ intermediate monocytes. In such a situation, decrease in the Slan+,CD14low,CD16+ non-classical monocyte fraction below 1.7% still supports CMML diagnosis. This robust, two-step flow cytometry assay identifies CMML with a very high sensitivity. Otherwise, detection of one or several acquired gene mutations with high variant allele frequency supports the diagnosis of CMML, oligomonocytic CMML or clonal monocytosis of clinical significance. Together, recent investigations support integration of flow cytometry analysis of peripheral blood monocyte subsets and new generation sequencing of a panel of 20-30 recurrently mutated genes in the diagnostic work-up of CMML.
Keywords: Chronic myelomonocytic leukemia; Diagnosis; Flow cytometry; Monocyte subsets; Somatic gene mutations.
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