This is a case of acinic cell carcinoma (AiCC) involving the parotid gland. AiCC comprises 10% of all malignant salivary gland tumors, and most often affects the parotid gland. These tumors are generally slow-growing and have a good prognosis. 

The tumor in question has a lobulated architecture, with solid nests of epithelioid cells containing granular, amphophilic cytoplasm that are separated by fibrovascular septae. Although serous acinar cells are the most frequent cell type seen in these tumors, many other cell types can be seen with varying frequencies (including intercalated duct type, vacuolated, nonspecific glandular, and clear cells). Within serous acinar tumor cells, zymogen granules are PAS-D positive.

Useful immunohistochemical (IHC) studies include SOX10 and DOG1, both of which are positive in AiCC. Additionally, 80% of tumors have a translocation involving NR4A3, thus an IHC for NR4A3 can serve as a highly specific marker.