Cytological features of mammary analogue secretory carcinoma of the parotid gland in a 15-year-old girl: a case report with review of the literature.

Mammary analogue secretory carcinoma (MASC) is a recently recognized tumor of salivary glands characterized by the ETV6-NTRK3 fusion gene. This tumor is very rare in children and adolescents. We report a case of MASC in a 15-year-old girl, the fifth youngest case so far reported. The patient complained of a left infra-auricular mass that gradually enlarged for a year. Fine-needle aspiration cytology/imprint cytology showed individual tumor cells that had faintly eosinophilic granular cytoplasm with secretion granules sometimes seen adjacent to the tumor cells. These cytological features overlapped between those of zymogen granule-poor acinic cell carcinoma (AciCC) and MASC. In addition to the case report, we present a review of the related literature with a focus on the cytological features of MASC. The differential diagnostic clues are also discussed.