Abstract
A case of intraductal papilloma of the male breast was studied by electron microscopy and immunohistochemistry. The major components of this lesion were the epithelial and myoepithelial cells. Intermediate cells showing ultrastructural features of both cell types were also observed. Squamous metaplasia was noted in many areas. Numerous intranuclear helioid inclusions were seen in the tumor cells. The features of this lesion are similar to those of papillomas of the female breast.