Background: Mammary analogue secretory carcinoma (MASC) is characterized by similar histologic, immunohistochemical, and molecular features with breast secretory carcinoma. MASC usually occurs in adults. Case report: 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. Conclusion: Typical histological, immunohistochemical, and molecular features are present in MASC occurring early in childhood.
Keywords: ETV6-NTRK3 fusion; Mammary analogue secretory carcinoma (MASC); pediatric patient; salivary gland tumor.