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Case Reports

Abstract

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, aggressive hematologic malignancy of the skin of elderly. It can mimic other hematopoietic neoplasms, posing a diagnostic challenge. Early recognition is critical given its leukemic dissemination and poor prognosis. We present a 78-year-old man presented with a 1.5-month history of an ulcerated right scalp lesion. Punch biopsy showed diffuse dermal infiltration by large blastoid cells with pleomorphic nuclei, open chromatin, prominent nucleoli, and abundant amphophilic cytoplasm with numerous mitosis, extending into the subcutis. Immunohistochemistry revealed expression of CD4, CD123, TCL1, and CD303 with weak CD56. In addition, the atypical cells strongly and diffusely expressed CD2 and CD7 and showed patchy weak to moderate CD3 in about 60% of cells. The cells were negative for MPO, TDT, lysozyme, CD5, CD8, and PAX5. CD68 showed a dot-like staining pattern. c-MYC immunohistochemistry was positive in 70% of cells. Bone marrow biopsy revealed cytologically similar involvement. Flow cytometry of peripheral blood demonstrated a related but slightly differing immunophenotype, negative for surface and cytoplasmic CD3. Cytogenetics revealed trisomy 8, an aberration more often seen in myeloid neoplasms. Despite atypical findings, including larger cells with a blastoid cytomorphology and prominent nucleoli, partial CD3 expression, and trisomy 8, the immunophenotype and clinical context support a diagnosis of BPDCN. The c-MYC positivity has been associated with the unusual immunoblastic cytomorphology, a variant reported in BPDCN with more aggressive clinical behavior. This case illustrates the morphologic and genetic heterogeneity of BPDCN and emphasizes the importance of a comprehensive evaluation in cutaneous hematolymphoid