Histiocytic and Dendritic Cell Neoplasms.

This article reviews the features of dendritic cells (DCs) of myeloid-derived, plasmacytoid, and follicle-associated types and tumors of these cells, as well as myeloid sarcoma. The morphologic and immunophenotypic features in this group of neoplasms is featured, including mature neoplasms such as Langerhans cell histiocytosis, its malignant counterpart Langerhans cell sarcoma, and S100-negative histiocytic proliferations. More immature or precursor malignancies in this group include myeloid and monocytic leukemias presenting in extramedullary tissues as well as the newly codified blastic plasmacytoid dendritic cell neoplasm. Although likely not related histogenetically to myeloid-derived DCs, mesenchymal-type lymph node tumors including follicular dendritic cell and fibroblastic reticulum sarcomas are also discussed. All of these neoplasms can exhibit a range of immunophenotypic and morphologic features that underscore the plasticity of the non-neoplastic precursors from which they are derived.