Abstract

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive malignant hematologic disorder arising from plasmacytoid dendritic cells, and previously known as CD56+ cutaneous hematodermic neoplasm. It is a very rare tumor that comprises less than 0.1% of all hematologic malignancies. The majority of patients with BPDCN present clinically with cutaneous lesions as the first sign of disease. At the time of diagnosis, most patients show evidence of leukemic dissemination. Extramedullary organ involvement may also occur. Immunophenotypic variability with aberrant marker profiles has been reported. We report a case of a TCF-4+ BPDCN, with negative CD56 expression in an 85 year-old woman, with multiple skin nodules. A skin punch biopsy from the left flank revealed a diffuse, monomorphous, and non-epidermotrophic cell infiltrate involving the entire dermis. The infiltrate was composed of intermediate-sized cells with immunoblastoid morphology (eccentric nuclei, vesicular and open chromatin, and prominent nucleoli). Frequent mitoses were present. The neoplastic cells were strongly positive for CD45 and co-expressed CD4, CD123, TCF-4, BCL-2, and CD10. The Ki67 proliferative rate was very high (90%). Negative immunostains included lineage specific markers such as CD20, CD19, CD3, lysozyme, and MPO. CD2, TdT, CD5, CD20, CD30, CD34, CD56, CD117, CD138, BCL-6, MUM-1, cyclin D1, PAX5, PAX8, GATA3, cytokeratin AE1/AE3, p63, S100, EBV, and in-situ hybridization for kappa and lambda were also negative. Lack of expression of CD56 is an unusual finding in BPDCN, reported in less than 8% of cases. This case illustrates the challenges encountered in the diagnosis of such entity, particularly in unusual morphologic variants and phenotype. The elucidation of molecular signatures and development of targeted therapies for its management have been recently introduced, and differ from acute myeloid leukemias. Hence, adequate diagnosis of BPDCN is critical for dermatopathologists.

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