Low grade adenosquamous carcinomas of the breast are epithelial and myoepithelial tumors

Abstract

Breast adenosquamous carcinomas are rare tumors that are categorized as subtypes of metaplastic carcinoma. They are composed of well-developed gland formation intimately admixed with solid nests of squamous cells immersed in a highly cellular spindle cell stroma. A low grade variant has been described to have a relatively indolent clinical course and an uncommon low grade histological pattern. However, some aspects of this tumor remain unclear, due to its rarity. Here, we report 25 cases of adenosquamous carcinoma of the breast: 14 cases of ’pure’ low grade adenosquamous carcinoma, seven cases of metaplastic carcinoma arising within foci of low grade adenosquamous carcinoma, one case of a composite tumor that associated adenosquamous carcinoma and phyllodes sarcoma with liposarcomatous stroma and three cases corresponding to high grade adenosquamous carcinoma. As results, we found that the glandular formations within foci of low grade and high grade adenosquamous carcinoma were surrounded by a certain amount of myoepithelial cells. Furthermore, spindle cells and heterologous elements of the stroma, in all tumor types, arose from the myoepithelial cells and expressed myoepithelial markers, basal keratins and a variable level of epidermal growth factor receptor expression.