BPDCN

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Blastic plasmacytoid dendritic cell neoplasm (BPDCN)

This is a rare diagnosis but one that presents some practical diagnostic difficulties since BPDCN is derived from myeloid cells and therefore shares morphological and some immunophenotypic characteristics which may overlap typical AML. Morphologically the primitive cells may resemble AML or have lymphoid morphology, with a skin rash present in most cases. NOTE other hematologic malignancies may share similar phenotypes with BPDCN, therefore diagnosis requires correlation with morphology, histopathology and clinical information.

Using standard diagnostic panels, cases of BPDCN generally have the following features:

• BPCDN typically have features of primitive phenotype: the cells typically lie in the "blast area" - with dim to moderate CD45 expression with low side scatter. CD7, TdT, CD38 and HLA-DR are frequently expressed. CD34 is characteristically absent
• Lineage-defining markers of myeloid, T or B cell are not expressed: i.e. there is no expression of MPO, CD14 or lysozyme; cCD3 is not expressed, and CD19 is not expressed (as well as CD20, cCD22, CD79a)
• One or more myeloid lineage-associated features may be detected: 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.

Diagnosis is then based on specific criteria:

Diagnostic criteria for BPDCN:

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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