Interventional cytopathologist perspective on the Milan System Classification: a study on 929 consecutive salivary gland fine-needle aspirations with a focus on challenging diagnostic categories

Background: Although the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) has improved the diagnosis and management of salivary gland lesions, determining the risk of malignancy (ROM) for AUS and SUMP categories remains challenging. We investigated the role of interventional cytopathologists in refining the differential diagnosis of these categories. Methods: We searched for salivary gland fine-needle aspirations (FNAs) performed at our Institution since the publication of the first edition of MSRSGC. In our Institution, salivary gland FNAs are performed by interventional cytopathologists only. We checked for the availability of histopathology reports to calculate the risk of neoplasm (RON) and ROM. Sensitivity, specificity, negative predictive value, and positive predictive values of our FNAs were assessed by focusing on the contribution of the AUS and SUMP categories to our diagnostic accuracy. Results: 929 salivary gland FNA diagnoses were retrieved. 37.02% FNAs had an available surgical follow-up. The ROM for each category was: 6% (ND); 0 (NN); 15.15% (AUS); 1.14% (NB); 24.4% (SUMP); 66.7% (SFM); and 94.74% (M). We observed a high level of concordance between our ROM data and the values proposed by the MSRSGC; higher accuracy (93.17%) and sensitivity (97%) were obtained when the AUS category was considered as a positive index for detecting salivary neoplasms; the best diagnostic accuracy (93.33%) was obtained when the SUMP category was considered as a negative index for malignancy. Conclusion: Interventional cytopathologists play an important role in salivary gland cytopathology, as demonstrated by the overt concordance between our ROM rates and those recommended by the MSRSGC.