In this analysis, we describe the clinical, hematologic, molecular and biologic characteristics of a cohort of 41 patients with MPN and a CMML-like phenotype (monocytosis ≥ 1 G/L + monocytes ≥ 10% in PB) and compare it to the characteristics of patients with JAK2-mutated CMML and PV patients without a CMML-like phenotype, respectively. This evidence concerns the gene JAK2 and acquired polycythemia vera.