A rare malignancy of the parotid gland in a 13-year-old Taiwanese boy: case report of a mammary analogue secretory carcinoma of the salivary gland with molecular study.

Mammary analogue secretory carcinoma (MASC) is a recently described malignancy of the salivary glands characterized by an ETV6-NTRK3 (EN) fusion gene. Morphologically, MASC is sometimes difficult to distinguish from acinic cell carcinoma. Consequently, identifying the chromosomal translocation is essential for diagnosis. We present a case of parotid gland MASC in a 13-year-old boy. To the best of our knowledge, this is the youngest case reported in the literature. Histologic evaluation showed a tumor composed of microcysts, tubular structures, solid nests, or papillary architecture, with secretions within the lumens of the cysts or tubules. Immunohistochemically, tumor cells showed diffuse positive staining of S-100 protein, cytokeratin 19, and vimentin. ETV6 rearrangement was detected by fluorescence in situ hybridization and EN fusion transcripts were verified by reverse transcription (RT-PCR) assay.