Resident Program - Case of the Month

April 2021 – Presented by Dr. Peter Michael Conner (Mentored by Dr. Regina Gandour-Edwards)

Discussion

Acinic cell carcinomas are malignant epithelial neoplasms of the salivary gland in which the neoplastic cells show serous acinar cell differentiation. These carcinomas tend to occur in women slightly more than men. There does not appear to be a predilection for particular ethnic groups and a wide age range of people are affected from young children to the elderly, although only four percent of patients are under 20 years old.

Acinic cell carcinoma typically begin as solitary, mobile masses in the parotid lesion. About a third of patients have painful nodules and small group (~5-10%) develop some facial paralysis. Most tumors are 1-3 cm in greatest dimension. On gross examination, they tend to be circumscribed, solitary nodules, but some masses are ill-defined with irregular borders and possibly multinodular. Their cut surface tends to appear tan to red and lobular; however, they can vary and appear soft to firm and solid to cystic.

Microscopically, acinic cell carcinomas shows a variety of growth patterns and cell types. The growth patterns include acinar, intercalated ductal, vacuolated clear, non-specific glandular and solid/lobular, microcystic, papillary-cystic, and follicular growth patterns. The tumor cells tend to be closely arranged in sheets, nodules, or aggregates, with possible spaces when a cystic growth pattern is present. Psammoma bodies are sometimes seen. Although a single cell type and growth pattern usually dominate, some tumors can have combinations of different types. Acinar cells and intercalated duct-like cells are most common, while clear cells tend to be rarer (only ~6% of all acinic cell carcinomas). A prominent lymphoid infiltrate of the stroma is often associated with these tumors.

The immunohistochemistry profile is non-specific. These tumors are positive for cytokeratin, carcinoembryonic antigen (CEA), and amylase. The zymogen granules in the neoplastic cells are often non-reactive with the anti-alpha-amylase immunostain but highlighted with PAS and are resistant to diastase digestion. Approximately 10% of tumors are S100 positive.

The prognosis of these carcinomas tends to be favorable. The average recurrence rate is about 35% and the metastatic and disease-associated death incidence is about 16%. Multiple recurrences and metastasis indicate a poorer outcome.

References

1. Barnes L., Eveson J.W., Reichart P., Sidransky D. (Eds.): World Health Organization Classification of Tumours. Pathology and Genetics of Head and Neck Tumours. IARC Press: 2005.
2. Lester D. R. Thompson, MD, Acinic Cell Carcinoma, https://app.expertpath.com/.  Updated May 25, 2019. Updated 4/17/20.
3. Ilayaraja V, Prasad H, Anuthama K, Sruthi R. Acinic cell carcinoma of minor salivary gland showing features of high-grade transformation. J Oral Maxillofac Pathol. 2014;18(1):97-101. doi:10.4103/0973-029X.131925
4. Al-Otaibi SS, Alotaibi F, Al Zaher Y, Al Zaher N, Dababo MA. High-Grade Transformation (Dedifferentiation) of Acinic Cell Carcinoma of the Parotid Gland: Report of an Unusual Variant. Case Rep Otolaryngol. 2017;2017:7296467. doi:10.1155/2017/7296467
5. Al-Zaher N, Obeid A, Al-Salam S, Al-Kayyali BS. Acinic cell carcinoma of the salivary glands: a literature review. Hematol Oncol Stem Cell Ther. 2009;2(1):259-64. doi: 10.1016/s1658-3876(09)50035-0. PMID: 20063555.