Cytopathological features of mammary analogue secretory carcinoma--review of literature.

Mammary analogue secretory carcinoma (MASC) is a recently described salivary gland tumor that morphologically resembles mammary secretory carcinoma and carries the identical ETV6-NTRK3 fusion gene. We report a surgical resected case of MASC in the parotid gland of a 41-year-old man. The cytological smears of a preoperative fine-needle aspiration showed many sheets and crowded clusters of monotonous epithelioid cells with mild atypia, suggestive of monomorphic tumor. Histologically, the tumor was composed of cuboidal cells with follicular, tubular, and solid structures, reminiscent of acinic cell carcinoma of follicular variant, which had been previously classified. This case had ETV6-NTRK3 fusion gene transcript confirmed by fluorescence in situ hybridization and reverse transcription polymerase chain reaction. In the cytological and histopathological diagnosis of monomorphic tumor of salivary gland, MASC needs to be taken into consideration as a differential diagnosis. Further immunohistochemical and gene analyses are needed in diagnosis of MASC.