Salivary gland-type tumors of the breast: a spectrum of benign and malignant tumors including "triple negative carcinomas" of low malignant potential.

Salivary gland-type neoplasms of the breast are uncommon and comprise of numerous entities analogous to that more commonly seen in salivary glands. The clinicopathologic spectrum ranges from benign to malignant but there are important differences compared to those of their salivary counterpart. In the breast benign adenomyoepithelioma is recognized in addition to malignant one, while in the salivary gland a histologically similar tumor is designated as epithelial-myoepithelial carcinoma without a separate benign subgroup. Mammary adenoid cystic carcinoma is a low-grade neoplasm compared to its salivary equivalent. It is also important to appreciate, that in contrast to “triple negative” conventional breast carcinomas with aggressive course, the majority of salivary-type malignant breast neoplasms behave in a low-grade fashion. Most of these tumours are capable of differentiating along both epithelial and myoepithelial lines, but the amount of each lineage-component varies from case to case, contributing to diagnostic difficulties. Well established examples of this group include pleomorphic adenoma, adenomyoepithelioma and adenoid cystic carcinoma. Another family of salivary gland-type mammary epithelial neoplasms is devoid of myoepithelial cells. Key examples include mucoepidermoid carcinoma and acinic cell carcinoma. The number of published cases of salivary gland-type mammary neoplasms is constantly increasing but some of the rarest subtypes like polymorphous low grade adenocarcinoma and oncocytic carcinoma are “struggling” to become clinically relevant entities in line with those occurring more frequently in salivary glands.