A Parotid Gland Mammary Analogue Secretory Carcinoma in a 4-Year-Old Boy: Case Report and Literature Review.

Mammary analogue secretory carcinoma (MASC) is characterized by similar histologic, immunohistochemical, and molecular features with breast secretory carcinoma. MASC usually occurs in adults. A 4-year-old boy presented with a right infra-auricular mass. Features of the tumor include solid, tubular, and papillary growth patterns, with homogenous eosinophilic secretions inside microcystic structures. Immunohistochemical stains showed strong, diffuse staining for CK7, S100, pan-TRK protein. P63 was positive in a peripheral pattern. Fluorescence in situ hybridization (FISH) analysis showed the characteristic ETV6-NTRK3 gene fusion. Typical histological, immunohistochemical, and molecular features are present in MASC occurring early in childhood.