Abstract

We highlight the utility of interferon regulatory factor 8 (IRF8), a novel marker of monocytic and dendritic cell lineages, in the diagnosis of a case of blastic plasmacytoid dendritic cell neoplasm (BPDCN) presenting initially in the skin, followed by systemic spread. A 60-year-old male with a previous history of myelodysplastic syndrome presented with cutaneous nodules on chest and scalp. Punch biopsy of a skin nodule showed a diffuse dermal infiltrate of atypical mononuclear cells. The neoplastic cells expressed CD4, CD56, and TdT but showed minimal reaction for TCL-1 and CD123, and were negative for CD34, CD117 and MPO. IRF8 performed in retrospect was strongly positive. Subsequent bone marrow involvement showed blastoid tumor cells with intense positivity for CD123, CD56 and CD4, which was supportive of the BPDCN diagnosis. BPDCN cases with weak or variable CD123 expression represent a potential diagnostic pitfall. In a recent study, 15 cases of BPDCN showed uniformly strong staining for IRF8, while CD123 was dim or negative in 4 of these 15 cases. We suggest IRF8 may be a useful marker for BPDCN, especially in cases with weak or variable expression of CD123 and TCL1.

Financial Disclosure:
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