Finding and Characterizing Mammary Analogue Secretory Carcinoma of the Salivary Gland

BACKGROUND: A new tumor entity of the salivary glands, mammary analogue secretory carcinoma (MASC) with ETV6-NTRK3 translocation, has recently been proposed. MASC was originally diagnosed as adenocarcinoma, not otherwise specified (ANOS), or acinic cell carcinoma (AciCC) by the current World Health Organization classification. We aimed to identify MASC cases by molecular tests, and to characterize their clinical, histological, and immunohistochemical features. METHODS: Thirty cases of MASC candidates were selected after review of 196 salivary gland tumors, and subjected to break-apart ETV6 fluorescence in situ hybridization (FISH), and immunohistochemical study for S100 protein, gross cystic disease fluid protein 15, DOG1, estrogen receptor, and progesterone receptor. RESULTS: Valid FISH results were obtained in 23 cases, and 13 positive cases were retrieved. MASCs were histologically varied, and the most frequent features observed in 10 cases were low-grade papillary/cystic/glandular patterns, intraluminal secretory materials, ovoid/wrinkled nuclei, and relatively abundant granular eosinophilic cytoplasms, corresponding to papillary-cystic or follicular types of AciCC. All cases showed diffuse immunopositivity for S100 protein. Three cases developed recurrences, but all patients remained alive. CONCLUSIONS: MASC could be a molecularly well-defined salivary gland neoplasm, encompassing some portions of AciCC and ANOS, but its histological spectrum and clinical implication require further investigation.