Plasmacytoid dendritic cells (pDCs) are part of the innate immune system and perform essential functions, such as antigen presentation and cytokine release. Malignant proliferations of pDCs are currently known as blastic plasmacytoid dendritic cell neoplasm (BPDCN) and were added in the 2008 revision of the World Health Organization (WHO) classification of hematological malignancies (Swerdlow et al., 2017). It is an aggressive disease defined by the clonal proliferation of blastic plasmacytoid dendritic cells precursors. Skin infiltration is almost universal, and bone marrow involvement, as well as that of lymphatic organs, is common. Blastic pDCs can be distinguished from their mature counterparts by morphology and expression of CD56 and CD33 (positive in 43% of BPDCN), among others. While the pathological diagnosis can be relatively straightforward when the clinical and pathological data show a matching picture, the coexistence of a monocyte-derived hematological malignancy makes the diagnostic process notably more difficult. Since these disorders are almost always CD4 and HLA-DR-positive and frequently express CD56, it can be very complex to establish whether the skin lesions are due to skin involvement by the monocytic malignancy or a BPDCN associated with it. In this setting, flow cytometry (FC) could be an important ancillary diagnostic tool. In this report, we describe a patient with CMML and BPDCN for whom FC played an essential role in distinguishing two phenotypically-similar, clonally-related, but ultimately different populations. We then conduct a systematic review of this association.

浆细胞样树突状细胞 (pDC) 是先天免疫系统的一部分，并执行基本功能，例如抗原呈递和细胞因子释放。pDC 的恶性增殖目前称为浆细胞样树突状细胞母细胞瘤 (BPDCN)，并被添加到 2008 年世界卫生组织 (WHO) 血液系统恶性肿瘤分类修订版中 (Swerdlow et al.,  2017 )）。它是一种侵袭性疾病，由原始浆细胞样树突状细胞前体的克隆增殖定义。皮肤浸润几乎是普遍的，骨髓和淋巴器官受累很常见。胚性 pDC 可以通过 CD56 和 CD33 的形态和表达（43% 的 BPDCN 阳性）等与成熟的 pDC 区分开来。虽然当临床和病理数据显示匹配时，病理诊断相对简单，但单核细胞来源的血液恶性肿瘤的共存使诊断过程明显更加困难。由于这些疾病几乎总是 CD4 和 HLA-DR 阳性并经常表达 CD56，确定皮肤病变是由单核细胞恶性肿瘤或与之相关的 BPDCN 引起的皮肤受累可能非常复杂。在这种情况下，流式细胞术 (FC) 可能是一种重要的辅助诊断工具。在本报告中，我们描述了一名患有 CMML 和 BPDCN 的患者，FC 在区分两个表型相似、克隆相关但最终不同的人群方面发挥了重要作用。然后，我们对该关联进行系统评价。