Risk of malignancy in "atypia of undetermined significance" category of salivary gland fine-needle aspiration: A bi-institutional experience

Background Many prior institutional and multi-institutional studies have applied the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) retrospectively to their specimens to determine the risk of malignancy (ROM) of each category. Most of these studies focused on general assessment of the system and risk classification. However, there seems to be less focus on the category of atypia of undetermined significance (AUS) that could be attributed to the low number of cases that could fit into this category. Herein, we present a bi-institutional experience with this category. Methods A computerized search of the databases was performed to identify all salivary gland fine-needle aspiration (FNA) in two institutions over a period of 12 years. The final diagnosis of each case was reclassified based on MSRSGC, and histology follow-up was retrieved. Results Sixty AUS cases (out of 1560 salivary gland FNA) were identified with a rate of 3.8%. Forty cases (66%) had a subsequent tissue material. Correlation with histology revealed that the estimated ROM is 37.5% (15/40) and the overall ROM is 25% (15/60). Fifty percent of the cases had a prominent lymphoid component and most commonly represented lymphomas, reactive lymph node or sialadenitis. Conclusion The AUS category is a heterogeneous group of lesions with predominant lymphoid-rich entities. Some variability exists between institutions with most having higher ROM than the suggested 20% by the MSRSGC atlas.