Clinicopathological analysis of 46 cases with CD4+ and/or CD56+ immature haematolymphoid malignancy: reappraisal of blastic plasmacytoid dendritic cell and related neoplasms

AimsIn this study, we aimed to investigate the clinicopathological features of CD4(+) and/or CD56(+) immature haematolymphoid malignancy (iHLM), including blastic plasmacytoid dendritic cell neoplasm (BPDCN). Methods and resultsWe analysed the clinicopathological features of 46 patients diagnosed consecutively with CD4(+)/CD56(+) iHLM. These cases were categorised into three groups based on their immunohistochemical expression of three plasmacytoid dendritic cell (pDC) markers [CD123, CD303 and T cell leukaemia/lymphoma (TCL1)]: cutaneous BPDCN (n=35), non-cutaneous BPDCN (n=6) and non-BPDCN-type CD56(+) neoplasms (n=5). Compared to non-cutaneous BPDCN, cutaneous BPDCN was associated with an older median age at onset (72years versus 45years, P<0.05), and higher positivity for CD4 (P<0.05), CD123 (P<0.05) and 2-3 pDC markers (89% versus 50%, P=0.05). Cutaneous BPDCN was divided into terminal deoxynucleotidyl transferase (TdT)(+) and TdT(-) subgroups, which did not differ in prognosis, although TdT(+) cases showed a lower median onset age (66years versus 79years, P<0.05) and higher frequency of extracutaneous lesions (P<0.05). Compared to the BPDCN groups, non-BPDCN-type CD56(+) neoplasm cases showed higher cytoplasmic CD3 positivity (P<0.05) and less frequent BCL-2 expression (P<0.05), and lacked cutaneous lesions. However, the survival curves overlapped. Notably, one case involved an unusual composite neoplasm, comprising CD56(+) lymphoblastic lymphoma and mature CD56(+) cytotoxic T cell lymphoma. ConclusionsOur present data support the recognition of cutaneous BPDCN as a homogenous entity, in contrast to the non-cutaneous form. Additional research is warranted to characterise non-BPDCN-type CD56(+) neoplasms.