BPDCN

Blastic plasmacytoid dendritic cell neoplasm (BPDCN)

Morphologically the primitive cells may resemble monocytic AML, or may have less easy to define or even lymphoic morphology. The cells typically lie in the "blast area" - with dim to moderate CD45 expression with low side scatter. A skin rash is present in most cases.

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Potential diagnostic difficulties

BPDCN is derived from myeloid cells and shares some morphological and some immunophenotypic characteristics with typical AML:

• Features of primitive phenotype: CD7 and TdT are frequently expressed but CD34 is most often absent
• Lineage-defining markers should not be expressed: MPO (as well as CD14 and lysozyme), cCD3, and CD19 (as well as CD20, cCD22, CD79a) should not be expressed
• Myeloid lineage-associated features are often found: expression of CD33 is relatively common (x%), CD117 may also be expressed (x%), CD13 may be found (x%). Therefore cases may fit the criteria to assign myeloid lineage
• It is therefore important that specific features of BPCDN are actively sought, particularly in cases with skin rash, absent CD34, and where diagnosis is based on expression of two myeloid markers

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Diagnostic criteria for BPDCN:

Bright expression of: CD56 is generally accompanied by CD36, CD38, CD43, CD71, and HLA-DR, To confirm the diagnosis look also for plasmacytoid dendritic cell (PDC) associated markers: .

Should express: bright CD56 and/or CD4

then

BPDCN associate markers:

CD123 expressed and one of: CD303, CD304, TCF4, TCL1

Or

CD123 not expressed but at least three of CD303, CD304, TCF4, TCL1 are expressed and context of negative markers (above) is met

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NOTE also other hematologic malignancies may share similar phenotypes, therefore diagnosis requires correlation with morphology, histopathology, clinical information to make a definitive diagnosis