Palisaded myofibroblastoma of the breast: a tumor closely mimicking schwannoma: report of 2 cases.

Myofibroblastoma is a relatively rare, benign mesenchymal tumor that typically occurs in the breast parenchyma. Unlike mammary-type myofibroblastoma, myofibroblastoma that primarily arises in the lymph nodes exhibits nuclear palisading, and the term palisaded myofibroblastoma has been proposed, accordingly. We report 2 unusual cases of myofibroblastoma of the male breast, which showed a predominant (>90% of the entire tumor) nuclear palisading and Verocay-like bodies. The present cases represent a hitherto unreported variant of mammary-type myofibroblastoma closely mimicking schwannoma. The diagnosis of myofibroblastoma was supported by immunohistochemical analyses showing a diffuse staining for desmin and CD34. In addition, the diagnosis of myofibroblastoma was confirmed in 1 case cytogenetically by the demonstration of the monoallelic loss of the FOXO1/13q14 locus by fluorescence in situ hybridization. Pathologists should be aware of this unusual variant of mammary myofibroblastoma to assure a correct diagnosis.