Resident Program - Case of the Month

Background:

Mammary Analogue Secretory Carcinoma (MASC) is a low-grade salivary gland carcinoma characterized by morphologic resemblance to mammary secretory carcinoma (1= WHO). It was originally described as a subset of acinic cell carcinomas but studies from 2008 to 2010 formally distinguished MASC as a separate entity from acinic cell carcinomas. Since then, over 200 cases have been reported.  MASC is usually found in adults with a mean age of 46.5 years and no sex predominance.

These tumors are most often found in the parotid gland, followed by the other areas in the oral cavity and the submandibular gland. Clinically, they normally present as painless, slow-growing masses.

Macroscopically, these tumors tend to be poorly defined and rubbery with a light-tan cut surface. In some cases, cyst formation with yellow-white fluid is seen.

Histologically, MASC’s may be either circumscribed or infiltrative with occasional perineural invasion.  Architecturally, these tumors can exhibit multiple different growth patterns including: microcystic/solid, tubular, follicular, and papillary-cystic structures.  They are often lobulated, with lobules separated by fibrous septa. Cytologically, the tumor cells are medium sized overall, with small to the medium round-oval nuclei. Their cytoplasm is eosinophilic and granular and/or vacuolated. Additionally, unlike acinic cell carcinomas, MASC tumor cells have no zymogen cytoplasmic granules. Other features such as mitotic figures and necrosis tend to be rare to absent.

Advances in molecular testing have shown that MASC tumors have a recurrent translocation t(12;15)(p13;q25), which results in an ETV6-NTRK3 gene fusion, which has not yet been seen on other salivary gland tumors. More recently, some cases of MASC have shown different fusion partners for ETV6 than NTRK3. Ultimately, MASC is considered an indolent malignancy; however high clinical stage and high-grade tumors are the main adverse prognostic factors.

References:

1. Bissinger O, Götz C, Kolk A, et al. Mammary analogue secretory carcinoma of salivary glands: diagnostic pitfall with distinct immunohistochemical profile and molecular features. Rare Tumors. 2017;9(3):7162. Published 2017 Oct 3. doi:10.4081/rt.2017.7162
   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5643951/
2.  EL-Naggar A.K., Chan J.K.C., Grandis J.R., Takata T., Slootweg P.J. (Eds): WHO Classification of Head and Neck Tumors (4^th Edition). IARC: Lyon 2017
3.  Sethi R, Kozin E, Remenschneider A, et al. Mammary analogue secretory carcinoma: update on a new diagnosis of salivary gland malignancy. Laryngoscope. 2014;124(1):188–195. doi:10.1002/lary.24254
   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4500055/
4. Todd M. Stevensand Vishwas Parekh (2016) Mammary Analogue Secretory Carcinoma. Archives of Pathology & Laboratory Medicine: September 2016, Vol. 140, No. 9, pp. 997-1001.
   https://doi.org/10.5858/arpa.2015-0075-RS
   https://www.archivesofpathology.org/doi/full/10.5858/arpa.2015-0075-RS