Salivary Gland Neoplasm of Uncertain Malignant Potential (SUMP) (Milan IVB) and Its Subgroups: A Multi-Institutional Analysis of Risk of Neoplasm and Malignancy.

Objectives: Fine needle aspiration (FNA) plays a crucial role in their initial assessment of salivary gland neoplasms. In the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC), the category of Salivary Gland Neoplasm of Uncertain Malignant Potential (SUMP) categorizes lesions with ambiguous features. This study aims to investigate the risk of neoplasm (RON) and risk of malignancy (ROM) within different subgroups of SUMP lesions using data from three large academic institutions.

Methods: We analyzed salivary gland (FNA) cases from three academic institutions post-MSRSGC implementation. Salivary gland FNA cases categorized as Milan IVB (SUMP) with subsequent surgical pathology follow-up were analyzed. Cases were divided into basaloid, oncocytic, and clear cell SUMP subtypes, with RON and ROM assessed and compared.

Results: Out of 1377 MSRSGC cases, 231 were SUMP (16.8%), with 101 subjected to surgical pathology follow-up. The overall ROM for SUMP was 20.8%, with variations of 10% to 29.5% observed amongst institutions, but no significant difference was observed among three institutions (p = 0.15). Basaloid and oncocytic SUMP displayed 17.1% and 20.5% ROM, respectively, without significant disparity. However, all clear cell SUMP cases were malignant on surgical resection.

Conclusions: This study highlights the variability in ROM for SUMP lesions and the significantly higher ROM in SUMP cases with clear cell features. These findings emphasize the importance of accurately subcategorizing SUMP lesions, particularly those with clear cell features, for appropriate clinical management.