Risk Assessment of Salivary Gland Cytological Categories of the Milan System: A Retrospective Cytomorphological and Immunocytochemical Institutional Study

Objective: The Milan System for Reporting Salivary Gland Cytology (MSRSGC) has been recently published to help communication between cytopathologists and clinicians. The aim was to assess our institutional experience with salivary gland fine needle aspiration cytology (FNAC) and the potential applicability of the MSRSGC for the estimation of the risk of neoplasm (RON) and risk of malignancy (ROM) for each category. Material and Method: Salivary gland FNAC procedures performed at NCI, Cairo University in a three-year period from 2016 to 2018 and had a corresponding histopathological diagnosis were included in the current study. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy were estimated. Histopathological final diagnosis was the gold standard. Cytological diagnoses were re-stratified according to MSRSGC with estimation of RON and ROM for each category. Results: A total of 118 cases were included in the current work. Sensitivity, specificity, PPV, NPV and accuracy were 84.6%, 88.2%, 78.6%, 91.8% and 87%, respectively. Cytological diagnoses were re-classified as non-diagnostic (2.5%), non-neoplastic (14.4%), atypia of undetermined significance (AUS) (6.8%), benign neoplasm (40.7%), salivary gland neoplasm of uncertain malignant potential (SUMP) (7.6%), suspicious for malignancy (8.5%), and malignancy (19.5%). The RON and ROM for each category were as follows: non-diagnostic (100%, 33.3%), non-neoplastic (17.6%, 11.8%), AUS (50%, 37.5%), benign neoplasm (97.9%, 2.1%), SUMP (88.9%, 44.4%), suspicious (90%, 60%), and malignancy (100% for each). Conclusion: The Milan System for Reporting Salivary Gland Cytology is a helpful classification system. The calculated ROM for each category of the studied cases was slightly above the published MSRSGC rates but still supported the recommended management for the patient.