Circulating monocyte partitioning and its alteration in hematological chronic neoplasms

Circulating monocyte partitioning refers to the relative quantification of the three main monocyte subsets in the peripheral blood, namely classical (cMo), intermediate (iMo), and non-classical (ncMo) monocytes, as assessed by flow cytometry, a new nomenclature described 15 years ago. This distribution is influenced by physiological variation as well as by certain therapeutic interventions. In addition, pathological alterations in monocyte partitioning are now well characterized in chronic hematological neoplasms. Most notably, a relative accumulation of cMo exceeding 94% of total circulating monocytes was identified more than a decade ago as a phenotypic hallmark of chronic myelomonocytic leukemia (CMML) and has since been incorporated into the most recent revision of the WHO classification. Altered monocyte partitioning has also been reported in patients with myelodysplastic syndromes (MDS) and myeloproliferative neoplasms (MPNs), highlighting its broader relevance across myeloid disorders.