Malignant rhabdoid skin tumor: an uncommon primary skin neoplasm. Ultrastructural and immunohistochemical analysis.

Rhabdomyosarcomatoid renal tumors were initially described as a subset of tumors in the National Wilms Tumor Study that had light microscopic features similar to rhabdomyosarcomas. Subsequent studies failed to reveal evidence of muscle differentiation, thus the genesis of the term "rhabdoid" tumor. Such renal tumors are rapidly lethal. Recent reports suggest the occurrence of tumors with similar morphology in other anatomic sites. We wish to report a primary malignant rhabdoid tumor of the facial skin with detailed immunohistochemical and ultrastructural studies. Vimentin was expressed in the tumor cells, but there was no immunoreactivity for cytokeratins, neurofilaments, muscle actin, synaptophysin, S-100, melanoma antigen HMB-45, epithelial membrane antigen, neuron specific enolase, Leu-7, leucocyte common antigen or lysozyme/alpha-1-antitrypsin. Ultrastructure revealed typical whorled cytoplasmic aggregates of intermediate filaments. These studies along with a literature review reveal the heterogeneous immunohistochemical profiles of these tumors with common morphologic features. While the histogenesis of these tumors remain uncertain, it is necessary to recognize that these aggressive neoplasms may occur primarily in the skin.