Answer: Primary acinic cell carcinoma

Histology: The tumor is nodular and sharply demarked. At low power, it has features of a lymph node including the presence of a florid chronic inflammatory infiltrate with numerous germinal centers. At higher power, the lymphoid infiltrate surrounds nests of tumor cells that form microcysts and follicles. The cells have vesicular nuclei with conspicuous nuclei, and basophilic cytoplasm with purple cytoplasmic granules.

Discussion: The presence of tumor epithelium in association with a florid lymphoid stroma raises 3 possibilities when dealing with salivary gland masses. In some salivary gland tumors, the lymphoid component represents an intrinsic component of the salivary gland tumors (e.g. sebaceous lymphadenoma, Warthins tumor). A second possibility is metastatic spread to an intraparotid lymph node. This usually occurs with high grade salivary carcinomas (e.g. salivary duct carcinoma) or metastatic spread from a cutaneous primary tumor of the ipsilateral face/scalp (e.g. melanoma, squamous cell carcinoma).

Finally, some tumors can induce a florid reactive lymphoid reaction sometimes referred to as a tumor associated lymphoid proliferation (TALP). TALP simply represents an immune reaction to the tumor, and it is quite commonly noted (to varying degrees) in acinic cell carcinomas and mucoepidermoid carcinomas. TALP easily lends itself to misinterpretation: it is sometimes misinterpreted as a lymph node harboring metastatic carcinoma. Even though this is an understandable error, it can have dramatic consequences in terms of upstaging of the tumor leading to overly aggressive patient management. Although the distinction between TALP and a true lymph node can be subtle, TALP reactions do not show evidence of well formed lymph node capsules with subcapsular sinuses.