Mammary analogue secretory carcinoma (MASC) is a rare low-grade malignant salivary tumor defined by t(12;15)(p13;q25) translocation resulting in ETV6-NTRK3 fusion transcript, detected by FISH or PCR. Clinically MASC presents as a slow growing, painless mass. The most common location is the parotid gland (70%); other sites include submandibular glands, lips, and the hard palate. It shares morphologic and genetic features with breast secretory carcinoma.

Histologically, MASC presents with patterns of solid, cystic, tubular, follicular or papillary architecture, and abundant mucinous to vacuolated eosinophilic secretions that lack zymogen granules. Low-grade, bland vesicular nuclei with prominent nucleoli are also present. Mitosis are infrequent (<3/10 high-power field [HPF]), and necrosis is usually absent.

Mucicarmine and PASD stains highlight luminal and intracytoplasmic mucin. Immunohistochemical staining is positive for: Mammaglobin, CK7, S100 protein, STAT5a, GCDFP15, MUC1, MUC4, GATA3; and negative for: p63, CK5/6, DOG1, SMA, calponin, CK14.

MASC is treated with surgical excision and neck dissection for clinically detected metastasis. Molecular targeted therapy may be used for ETV6-NTRK3[+] tumours.