As other haematological neoplasms can share morphological and immunophenotypic features with BPDCN (especially AML with monocytic differentiation, which can carry CD4, CD56, and CD123 [41,60,61], extensive immunohistochemical and/or genetic analysis is required before a definitive diagnosis of BPDCN can be made. The gene discussed is NCAM1; the disease is CD4+/CD56+ hematodermic neoplasm.