Fine-needle aspiration cytology of mammary analog secretory carcinoma of the parotid gland: A diagnostic conundrum

Mammary analog secretory carcinoma (MASC) is a recently described salivary gland neoplasm with the parotid gland being the most common location, defined by the t (12;15) (q13;q25) translocation that results in ETV6-NTRK3 gene fusion product. Histological evaluation revealed an extraductal unencapsulated solid and cystic neoplasm with varied architectural patterns such as tubular, papillocystic, microcystic, and cribriform patterns [Figure 2]a. The constituent cells were small-to-medium-sized with oval-to-round nuclei with pale chromatin, an occasional small nucleolus, and abundant pink to eosinophilic bubbly cytoplasm [Figure 2]b. The microcysts contained luminal eosinophilic colloid-like secretions [Figure 2]b. The tumor showed strong diffuse expression of CK8/18, PANCK, CK7, EMA, S-100, GCDFP-15, and negative for p63 and DOG-1 [Figure 2]c and [Figure 2]d. Mucicarmine stain highlighted the intracellular and extracellular mucin vacuoles. The cytological features along with clinical findings, immunohistochemical studies complemented by molecular studies on cell block can produce a more accurate preoperative diagnosis of MASC.