Blastic plasmacytoid dendritic cell neoplasm of skin, a rare dermatohematologic malignancy-A case report.

Key Clinical Message: Blastic plasmacytoid dendritic cell neoplasm is a rare hematologic malignancy and appropriate diagnosis encounters difficulties in both clinical and pathologic aspects. This case report aims to present a clinical case to help familiar clinicians and pathologists with this rare entity. Abstract: Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an uncommon hematologic malignancy. Because of the rarity of the disease and aggressive behavior, we present this case. A 71-year-old man presented with a forehead ulcerated skin lesion. On histopathologic examination, pan-dermal atypical mononuclear infiltrate, consisting of small-medium sized cells with fine chromatin pattern was seen without epidermotropism which were immunoreactive for CD123, CD56, TdT and CD4, while negative for CD3, CD20, and MPO that confirmed the diagnosis of BPDCN. BPDCN is a highly aggressive hematologic malignancy derived from plasmacytoid dendritic cells. Male-to-female ratio is 3.3:1. Skin involvement can present as either an isolated purplish nodule or disseminated purplish nodules or papules or macules. On microscopic examination, skin involvement is characterized by monomorphic infiltrates of immature neoplastic cells with blastoid morphology, involving the superficial and deep dermis, often with extension into the subcutis with epidermal spare. Immunophenotyping shows usually positive reactions for CD123, CD45, CD4, CD56, TCL1, CD2AP, CD43, BCL2, TdT, Granzyme B, and TCF4, whereas tumor cells are negative for CD3, CD19, CD20, MPO, CD13 and Lysozyme. Differential diagnoses of BPDCN include myeloid sarcoma, myelomonocytic leukemia, mature plasmacytoid dendritic cell proliferation (MPDCP) and Merkel cell carcinoma. Pathologists ought to be familiar with this WHO entity for early disease diagnosis, because of disease rarity and diagnosis difficulties.