Blastic plasmacytoid dendritic cell neoplasm: Cytopathologic findings

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, aggressive hematopoietic neoplasm, which in the past was also known variously as blastic NK cell lymphoma, agranular CD4+ natural killer cell leukemia, and CD4+/CD56+ hematodermic neoplasm. BPDCN is now believed to arise from plasmacytoid dendritic cells, but its exact etiology is still unknown. We report here on the cerebrospinal fluid (CSF) cytology of a BPDCN, a hypercellular specimen comprised of malignant, singly dispersed cells with scant to moderate amounts of pale blue, agranular cytoplasm, and uniform round to oval nuclei, fine chromatin, prominent nucleoli, occasional cytoplasmic microvacuoles, and pseudopodia. Neither mitoses nor karyorrhexis were identified. Flow cytometry of the CSF demonstrated that the malignant cells expressed bright CD45, HLA-DR and CD33, dim CD4, heterogeneous CD56, and partial CD123. The importance of clinical, histopathological, and phenotypic correlation is emphasized. Clinical and histopathological correlation and a literature review are also presented. The poor clinical outcome makes it important to accurately report this rare tumor in a CSF specimen.