Abstract

Blastic plasmacytoid dendritic cell neoplasm (BPDCN), an aggressive neoplasm derived from precursors of plasmacytoid dendritic cells, is typically CD4+/CD56/ CD123+/ TCL1+. There is immunophenotypic overlap with myeloid leukemias. In cutaneous involvement by BPDCN, CD4 + medium-sized blast-like cells permeate the dermis, potentially simulating T-cell lymphoma. Metachronous or synchronous leukemic presentations are common, requiring work up/monitoring for leukemia. We present a challenging case of BPDCN. On routine follow up for skin cancer a 70-year-old male was found to have a yellowish pink papule on his left medial cheek, which was biopsied to exclude cancer. He had a history of congestive heart failure and, due to progressive dyspnea and fatigue, was hospitalized two weeks later, where pancytopenia was noted. The biopsy revealed an endophytic squamous proliferation of glassy infundibular-type epithelium, felt to be pseudoepitheliomatous hyperplasia or a keratoacanthomatous neoplasm, surrounded by a dense infiltrate of blast-like mononuclear cells with single cell necrosis. The infiltrate was diffusely CD4+/CD123+/CD43+/CD68+, with scattered large TCL1+ cells. The atypical cells were CD3-/CD2-/CD7-/CD8-/CD56-/ CD163-/MPO-/TdT-/ CD34/CD117-/CD20-/CD19-/CD30-/EBER. A diagnosis of leukemia cutis was made, favoring the rare CD56 negative subtype of BPDCN. Bone marrow examination revealed leukemia cutis, the subtype of which is still being determined. This case is unique and challenging due to negative CD56 expression, but this has been reported in BPCDN. A concomitant squamous proliferation is seen in CD30+ lymphoproliferative disorders but is rare to absent in reported BPDCN. This collision of neoplasms may be akin to that seen with chronic lymphocytic leukemia and non-melanoma skin cancers.

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