Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare haematological malignancy characterized by the clonal proliferation of immature or precursors of plasmacytoid dendritic cells (PDC), also known as professional type I interferon producing cells.1 This neoplasm was originally recognized in 19942 and the uncertainty regarding its histogenesis was reflected by the several changes of name, that included agranular CD4+ natural killer cell leukemia,3 blastic natural killer leukemia/lymphoma,4 agranular CD4+CD56+ hematodermic neoplasm5 or tumor.6 In 2001 the World Health Organization (WHO) classification of tumors of hematopoietic and lymphoid tissue coined the term blastic NKcell lymphoma on the basis of the blastic cytology, and the expression of CD56 in the absence of other lineage specific markers. A relationship to plasmacytoid dendritic cells was hypothesized first by Lucio et al. in 19997 and subsequently confirmed by several studies.5,8-13 The term blastic plasmacytoid dendritic cell neoplasm was introduced in 2008 by the updated WHO classification (4th edition).14 The clinical hallmarks of BPDCN are predominant cutaneous involvement, with subsequent or simultaneous extension to bone marrow and peripheral blood. Systemic dissemination and short survival are characteristic. Morphologically tumor cells show an immature “blastic” appearance; the diagnosis rests upon the demonstration of CD4 and CD56, together with markers more restricted to PDC (such as BDCA-2, CD123, TCL1, CD2AP and BCL11a) and negativity for lymphoid, NK and myeloid lineage- associated antigens.