Impact of Incorporating Clinical and Radiological Follow-Up Data on Risk of Malignancy Estimation in the Milan System for Reporting Salivary Gland Cytopathology

Summary: Introduction: The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) aims to standardize the reporting of salivary gland fine needle aspiration (FNA) and to provide estimates for the risk of malignancy (ROM) to assist clinical decision-making. However, ROM estimates in the literature often suffer from selection bias due to reliance on the subset of lesions with surgical follow-up. Materials and Methods: We retrospectively analyzed 1196 salivary gland FNAs between July 2020 and April 2024. MSRSGC was assigned based on the classification and diagnosis for each case. Data on histology, clinical, and radiological follow-up were collected from electronic medical records (EMR), and a composite follow-up outcome (benign, malignant, stable, or uncertain malignant potential) was assigned to each case. Data was analyzed using R v4.3, focusing on the indeterminate categories (I, III, IVB, V), comprising 185 FNA. Subsequent histology was available for 92 cases, while 145 had composite follow-up longer than 1 year. Results: Table 1 summarizes ROM estimates. Incorporating clinical and radiological follow-up data led to significantly lower estimated ROM compared to histology alone. ROM varied among different types of salivary gland tumors of uncertain malignant potential (SUMP), with oncocytic SUMP having a lower ROM than basaloid and mixed SUMP having a higher ROM (Table 2) Conclusions: Our findings underscore the importance of incorporating clinical and radiological follow-up data in estimating ROM in indeterminate MSRSGC categories. This study questions prior ROM estimates for SUMP types and warrants further investigation. Analysis of a 10-year dataset with over 7000 salivary gland FNAs at our institution is underway to provide additional insights.