Salivary Gland–like Tumors of the Breast Express Basal-type Immunohistochemical Markers

Abstract

Salivary gland-like tumors represent approximately 2% of primary breast carcinomas. These special histologic subtypes are characteristically negative for ER, PR, and HER2 (triple negative), and include adenoid cystic carcinoma, mucoepidermoid carcinoma, acinic cell carcinoma, and polymorphous low-grade adenocarcinoma. Approximately 75% of triple-negative breast carcinomas belong to the basal-like subtype by gene expression profiling. Immunohistochemical panels that include basal-like markers such as EGFR, CK5/6, p-cadherin, p63, and c-kit provide useful surrogates to gene expression arrays for classification of triple-negative breast cancers into the basal-like subtype. The purpose of this study was to explore the expression of these markers in salivary gland-like tumors of the breast. Excisional specimens from 10 untreated invasive triple-negative mammary carcinomas with salivary gland-like morphologies were evaluated for the immunohistochemical expression of EGFR, CK5/6, p-cadherin, p63, and c-kit using formalin-fixed, paraffin-embedded tissue and the L-SAB detection method. On the basis of morphology, 5 carcinomas were classified as adenoid cystic, 3 as mucoepidermoid, and 2 as polymorphous low grade. All of the adenoid cystic carcinomas, mucoepidermoid carcinomas, and polymorphous low-grade adenocarcinomas showed strong and diffuse expression of CK5/6, p-cadherin, and p63. EGFR was expressed weakly in adenoid cystic carcinomas and polymorphous low grade, whereas mucoepidermoid carcinomas had a stronger expression. C-kit was expressed in adenoid cystic carcinomas and low-grade polymorphous, but only weakly positive in mucoepidermoid carcinomas. Adenoid cystic, mucoepidermoid, and polymorphous low-grade carcinomas of the breast express immunohistochemical markers that characterize the intrinsic basal-like subtype of breast cancer.