The cytopathologic features of mammary analog secretory carcinoma and its mimics.

Mammary Analogue Secretory Carcinoma (MASC) is a newly recognized neoplasm of the salivary gland, first described in 2010. This tumor harbors a unique translocation, t(12;15)(p13;q25) that results in the fusion of ETV6 with NTRK3 which produces a transformative chimeric tyrosine kinase. To date, few cases of MASC sampled by fine needle aspiration have been reported. Cytologically, MASC can be confused with other oncocytic salivary gland tumors, including Warthin-tumor, acinic cell carcinoma (AciCC) and mucoepidermoid carcinoma. It is characterized by a monomorphic population of lesional cells with round nuclei, prominent nucleoli and abundant, eosinophilic foamy cytoplasm; forming papillary groups with transgressing vessels. Though, based on cytomorphology alone, the definite diagnosis can be challenging, in conjunction with available clinical clues (i.e. male patient, extra-parotid site) MASC should be included in the differential diagnosis of FNA specimens diagnosed as oncocytic salivary gland neoplasms or suspicious for AciCC. Here we present a case of MASC with FNA sampling at our institution.