Analysis of Histologic Follow-Up and Risk of Malignancy for Salivary Gland Neoplasm of Uncertain Malignant Potential Proposed by the Milan System for Reporting Salivary Gland Cytopathology

Abstract

BACKGROUND: The Milan System for Reporting Salivary Gland Cytopathology is a tiered classification scheme that includes 6 diagnostic categories. Neoplasm, which is 1 of the 6 proposed categories, consists of benign neoplasm and neoplasm of uncertain malignant potential (NUMP). NUMP is reserved for a salivary gland neoplasm without clear distinction between benign and malignant. The objective of this study was to assess the risk of malignancy (ROM) of NUMP. METHODS: A retrospective analysis was conducted on 656 salivary gland fine-needle aspiration specimens from 2010 to 2016. Cases that qualified as NUMP and had follow-up surgical resections were reviewed and reclassified into basaloid neoplasm (BN) and salivary gland neoplasm with predominant oncocytic cell (SGNOC) groups. The ROM for each group was calculated. Fifty-four salivary gland fine-needle aspirations of NUMP that had surgical follow-up were identified, which included 29 BNs and 25 SGNOCs. RESULTS: Histologic follow-up for the BN group identified 14 cellular pleomorphic adenomas, 5 basal cell adenomas, 2 benign cystadenomas, 3 adenoid cystic carcinomas, 3 epithelial and myoepithelial carcinomas, 1 basal cell adenocarcinoma, and 1 myoepithelial carcinoma. Histologic follow-up for the SGNOC group revealed 7 nodular oncocytoses, 6 Warthin tumors, 5 oncocytomas, 1 sebaceous adenoma, 1 mucinous cystadenoma, 2 acinic cell carcinomas, 2 mucoepidermoid carcinomas, and 1 mammary analog secretory carcinoma. The ROM was calculated at 24.1% for the NUMP category overall (27.6% for BNs and 20.0% for SGNOCs). CONCLUSIONS: The ROM of the SGNOC group is similar to that of the BN group but lower than the ROM (35%) proposed by the Milan system. Cancer Cytopathol 2018;126:490-97. © 2018 American Cancer Society.