Cytomorphology Subtypes of the Salivary Gland Neoplasm of Unknown Malignant Potential (SUMP) Category in the Milan System and Histologic Correlation.

Abstract

Introduction: The Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) offers a reliable framework for stratifying malignancy risk of salivary gland lesions. Salivary gland neoplasms of uncertain malignant potential (SUMP) are a heterogeneous group of lesions displaying neoplastic characteristics that cannot be definitively categorized as benign or malignant. This study evaluates the cytomorphologic characteristics of SUMP cases at our institution and correlates them with final histopathological outcomes.

Material and methods: A retrospective review of all SUMP cases diagnosed in our department from January 2018 to October 2024 was conducted. Cytology slides available were re-examined by three experienced cytopathologists and categorized into four subgroups based on key cytomorphologic features: (1) basaloid, (2) oncocytic, (3) clear cell, and (4) mixed features. Surgical follow-up diagnoses performed at our institution were collected.

Results: From a total of 495 salivary gland FNA specimens, 39 (7.9%) were initially diagnosed as SUMP. After reassessment, 35 cases of SUMP were confirmed, and 27 had surgical follow-up. The overall risk of a neoplastic lesion was 92.5%, with a malignancy risk of 18.5%. The subgroup with clear cell features exhibited the highest risk of malignancy, at 66.7%, while the oncocytic/oncocytoid and basaloid subgroups showed low malignancy risk (up to 10%).

Discussion and conclusion: This study supports the subclassification of SUMP lesions based on key cytomorphologic features, as it aids in refining the risk assessment and management of these ambiguous lesions. The identification of high-risk groups can help guide clinical decisions regarding follow-up.