Cytopathologic features of mammary analogue secretory carcinoma

Mammary analogue secretory carcinoma (MASC) is a recently described salivary gland neoplasm that is defined by ETV6-NTRK3 gene fusion. To the best of the authors' knowledge, only rare case reports of the cytopathologic features of MASC have been published to date.

A wide variety of archival salivary gland tumors were tested for ETV6 translocation by break-apart fluorescent in situ hybridization. Positive cases with preoperative fine-needle aspiration (FNA) specimens or intraoperative touch preparations were retrieved from the archives of The Johns Hopkins Hospital. All smears were reviewed and the cytologic characteristics were described.

Five cases of MASC with cytopathologic material (4 FNA specimens and 1 touch preparation) were identified. The cases occurred in 3 men and 2 women ranging in age from 21 years to 78 years (mean, 52 years). On the cytologic smears, the MASCs were variably cellular and exhibited 2 different architectural patterns: 1) intact tissue fragments with isomorphic cells arranged in a sheet-like or papillary configuration; and 2) dispersed and dissociated cells with a mostly "histiocyte-like" appearance with large cells containing abundant vacuolated cytoplasm. No matrix tissue or stromal spindled cells were present. The cells did not display acinic differentiation in the form of cytoplasmic zymogen granules. In each case, the preoperative FNA correctly identified a neoplasm, and the most frequent diagnostic considerations were acinic cell carcinoma, mucoepidermoid carcinoma, and pleomorphic adenoma.

MASC is a newly described salivary gland tumor that should be considered in the differential diagnosis of low-grade salivary gland neoplasms. Its cytologic features overlap considerably with those of other tumors, especially acinic cell carcinoma and mucoepidermoid carcinoma.