The role of the Milan System for Reporting Salivary Gland Cytopathology: A 5-year institutional experience

BACKGROUND: Fine-needle aspiration (FNA) is widely accepted in the preoperative management of salivary gland lesions. The proposed Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) aims to standardize reporting terminology. Studies regarding the risk of malignancy (ROM) for the proposed categories continue to evolve. The current retrospective study applied the MSRSGC to assess ROM for salivary gland lesions and focused on the “indeterminate” categories. METHODS: A total of 627 salivary gland FNA specimens obtained from 2011 through 2016 were retrieved, with follow-up available for 373 cases. The original diagnoses were recategorized using MSRSGC by 2 independent cytopathologists as: 1) non-diagnostic; 2) non-neoplastic; 3) atypia of undetermined significance (AUS); 4a) benign neoplasms; 4b) salivary gland neoplasm of uncertain malignant potential (SUMP); 5) suspicious for malignancy (SFM); and 6) malignant. The ROM and overall ROM for each diagnostic category were determined, with characterization of “indeterminate” (AUS, SUMP, and SFM) lesions. RESULTS: There was near-perfect agreement regarding categorization (626 of 627 cases; 99.8%) between the 2 cytopathologists, with discordance observed for 1 case. The sensitivity, specificity, negative predictive value, and positive predictive value of salivary gland FNA specimens at the study institution were 79%, 98%, 94%, and 92%, respectively. The ROM for non-diagnostic, non-neoplastic, benign neoplasms, AUS, SUMP, SFM, and malignant were 6.7%, 7.1%, 38.9%, 5.0%, 34.2%, 92.9%, and 92.3%, respectively. The indeterminate category had an overall ROM of 47.1%. CONCLUSIONS: The MSRSGC is a valuable tool that can help to standardize reporting and stratify cases preoperatively. Having a better understanding of the indeterminate diagnoses will help further refine risk classification criteria. Cancer Cytopathol 2018.