BPDCN

'Blastic plasmacytoid dendritic cell neoplasm (BPDCN)

Morphologically the primitive cells may resemble monocytic AML and typically lie in the "blast area" with dim to moderate CD45 expression with low side scatter

The cells will generally lack definite lineage markers of myeloid cells, although expression of CD33 is relatively common, with CD117 expressed in some cases allowing potetial confusion with AML. MPO is not expresssed

Similarly CD7 expression is common and TdT expression is relatively frequent, but CD3 is not expressed

Expression is expected for: CD4, CD56 (bright), CD36, CD38, CD43, CD71, HLA-DR, Plasmacytoid dendritic cell (PDC) associated markers: CD123, CD303, CD304, TCF4, TCL1 .

WHO diagnostic criteria allow BPDCN to be diagnosed:

• in the presence of CD123 and one other PDC-associated marker in addition to CD4 and/or CD56,
• in the presence of three PDC-associated markers and the absence of CD34 and other cell type-specific markers including CD3, CD14, CD19, lysozyme, and MPO.

Given the presence of other hematologic malignancies with similar phenotypes, correlation with histomorphology, clinical information and IHC studies is always necessary to make a definitive diagnosis of BPDCN.