Unmasking MASC: bringing to light the unique morphologic, immunohistochemical and genetic features of the newly recognized mammary analogue secretory carcinoma of salivary glands

Abstract

Mammary analogue secretory carcinoma (MASC) is a recently described salivary gland neoplasm that is characterized by its striking morphologic and molecular similarities to secretory carcinoma of the breast. This review highlights the characteristic clinical, histologic, immunophenotypic, and molecular features of MASC, and draws attention to the differential diagnosis of this increasingly recognized tumor.

Fig. 1

Mammary analogue secretory carcinomas (MASCs) usually exhibit microcystic (a) and/or papillary-cystic (b) growth patterns. Eosinophilic secretory material is present in the microcystic and macrocystic spaces

Fig. 2

At low-power, MASC (a) is histologically indistinguishable from this microcystic-patterned ACC (b). However, at high-power, MASC (c) lacks the basophilic cytoplasmic granules that define ACC (d)

Fig. 3

The cells of mammary analogue secretory carcinoma (MASC) may have a vacuolated cytoplasm that can impart a somewhat clear cell appearance (a). MASC cells and secretions characteristically exhibit strong immunostaining for S-100 (b) and mammaglobin (c). ETV6 break-apart FISH demonstrates one intact gene (i.e., orange and green together creating a yellow fusion signal) and one rearranged ETV6 gene (d)