Proliferation of monocytes (MO) occurs in reactive conditions as well as in myeloid neoplasm with clonal monocytosis such as chronic myelomonocytic leukemia (CMML). CMML is a type of clonal hematopoietic disease characterized by a sine qua non condition: sustained peripheral blood monocytosis (absolute monocytes count from ≥1 X109/L, to ≥0.5 X109/L with monocytes accounting for ≥10% of the peripheral white blood cells), accompanied by overlapping changes in bone marrow of myelodysplasia and myeloproliferation, <20% blasts and presence pf clonality. In CMML, there is an inherent risk for leukemic transformation (15% over 3-5 years). The French-American-British (FAB) co-operative group, created in 1976, proposed a uniform system of classification and nomenclature of hemato-oncologic malignancies. Classification of hematopoietic neoplasms is essential for making proper evidence-based treatment decisions and accurately assessing prognosis.

单核细胞（MO）的增殖在反应性条件以及克隆性单核细胞增多症如慢性粒单核细胞白血病（CMML）中都会发生。CMML是一种以持续外周血单核细胞增多（绝对单核细胞计数≥1 X10⁹/L，或外周白细胞的5%～10%，单核细胞占比≥10%）为特征的克隆性造血疾病，并伴有骨髓中髓系发育异常和增殖性疾病重叠的变化、原始细胞比例小于20%以及存在克隆性的特点。在CMML中，有向白血病转化（3-5年内约15%）的内在风险。法国-美国-英国（FAB）合作小组于1976年成立，提出了血液肿瘤分类和命名的一致系统。对造血系统肿瘤进行分类对于做出基于证据的治疗决策以及准确评估预后至关重要。