Amyloid-rich low grade adenocarcinoma of the parotid: fine-needle aspiration cytology with histologic correlations.

Amyloid deposits are unexpected in salivary gland tumors. A 60-year-old woman presented with a 1.8 cm, slow-growing parotid mass. Both fine-needle aspiration and frozen section were misinterpreted as pleomorphic adenoma. The final pathology was amyloid-rich low grade adenocarcinoma of the parotid gland. The aspirates consisted of three components: mucin, amyloid, and tumor cells. The mucin was unusually thick, stringy, and metachromatic. The amyloid presented as innumerable concretions scattered solitarily or in small jigsaw puzzle-like aggregates, individually wrapped by tumor cells. The tumor cells had bland oval nuclei and scant-to-abundant cytoplasm, arranged in loosely cohesive small sheets. On histology, the tumor cells were arranged in interconnecting monolayered glands of a wide range of size with small patches of cellular regions composed of plump tumor cells. As the luminal mucin and amyloid deposits enlarged, the lining tumor cells became thin and flat. The glandular lumen molded amyloid concretions into different shapes and sizes. Atrophic or pyknotic tumor cells outlined the amyloid concretions with concentric laminations, reminiscent of corpora amylacea. Alcian blue positive luminal mucin, associated with newly formed amyloid, was present in mucinous regions of the tumor. This is the first description of cytologic features of amyloid-rich low grade adenocarcinoma of the parotid and the second case in the pathology literature. The literature of amyloid-rich tumors was reviewed and the implication of the presence of abundant amyloid on the death of tumor cells suggested.