Application of the Milan System for Reporting Salivary Gland Cytopathology: A 10-Year Experience in a Single Japanese Institution

Objective: The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) is a recently published evidence-based categorization system for salivary gland fine-needle aspiration (FNA). We applied MSRSGC to Japanese cases and evaluated its utility. Study Design: A total of 480 FNA cases were reviewed. We recategorized each case into one of the MSRSGC categories. The risk of neoplasm (RON) and the risk of malignancy (ROM) for each diagnostic category in MSRSGC, and the sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) for malignancy and for neoplasms were calculated for cases with histological follow-up. In addition, the overall ROM (O-ROM) was calculated for all FNA cases. Results: RON, ROM, and O-ROM rates were as follows - non-diagnostic: 51.3, 5.1, and 1.0%; non-neoplastic: 0, 0, and 0%; atypia of undetermined significance: 83.9, 12.9, and 7.3%; neoplasm, benign: 100, 0, and 0%; salivary gland neoplasm of uncertain malignant potential: 100, 32.1, and 23.7%; suspicious for malignancy: 100, 85.7, and 60%; and malignant: 100, 100, 81.8%. The sensitivity, specificity, and accuracy with (without) indeterminate cases for malignancy were 65 (100), 99 (99), 92% (99%) and PPV and NPV were 96 and 100%, respectively, and those for neoplasms were 84 (100), 100 (100), 85% (100%), and PPV and NPV were 100 and 100%, respectively. Conclusions: The MSRSGC is useful for stratification of ROM and for promoting the performance of salivary gland FNA. The MSRSGC could be easily introduced in Japan and may improve the Japanese salivary gland FNA status.