Mammary analogue secretory carcinoma of parotid: Is preoperative cytological diagnosis possible?

Mammary analogue secretory carcinoma is a recently recognized tumor of salivary gland with characteristic t(12;15)(q13;q25) that results in ETV6-NTRK3 fusion product. Distinguishing mammary analogue secretory carcinoma from other salivary gland tumors is important. Present study highlights cytologic findings in three cases of mammary analogue secretory carcinoma of parotid which facilitate preoperative diagnosis with the aid of ancillary diagnostic techniques. Fine needle aspiration cytology of parotid was performed on three cases after clinical examination. Immunocytochemistry for mammoglobin and S100 were performed. Parotidectomy was done in all cases. The corresponding hematoxylin and eosin stained slides and blocks of all cases were studied. Molecular analysis was done in one of the cases. Cases 1 and 3 revealed uniform atypical epithelial cells arranged in branching papillary pattern with few cells in microcystic pattern. Case 2 showed atypical cells arranged mainly in loose clusters and few singly dissociated. Individual cells revealed round nuclei, vesicular chromatin, prominent nucleoli and abundant finely vacuolated cytoplasm with metachromasia prominent in May-Grunwald-Giemsa smear (case 3). Characteristic hob-nail cells covering papillae were observed in cases 1 and 3. Immunocytochemistry showed strong positivity for mammoglobin and S100 thereby confirming the diagnosis of mammary analogue secretory carcinoma preoperatively. The diagnosis was in concordance with surgical specimen. Also, characteristic ETV6-NTRK3 translocation was confirmed in case 1. Increased awareness and high index of suspicion is necessary for the upfront diagnosis, more so for the papillary variant of mammary analogue secretory carcinoma. Immunocytochemistry aids in confirming this preoperative diagnosis, based on which treatment can be planned. Diagn. Cytopathol. 2016;44:519-525.