Preliminary diagnostic criteria for distinguishing metaplastic Warthin tumors from mucoepidermoid carcinomas rich in lymphoid stroma

OBJECTIVE: This study aimed to analyze the clinicopathological and immunohistochemical profiles of unconventional Warthin tumors and mucoepidermoid carcinomas. METHODS: Eleven low-grade salivary gland tumors with Warthin-like features were analyzed. Group A (n=6) showed a double-layered oncocytic epithelium in less than 50% of the epithelial cells, whereas Group B (n=5) lacked this feature. Additionally, five conventional Warthin tumors and ten conventional mucoepidermoid carcinomas were analyzed as reference groups. Immunohistochemical staining was performed for cytokeratins (types 5/6, 7, and 14), p63, mitochondrial antigens, and Ki-67. Expression patterns were compared between groups. RESULTS: Group A exhibited an oncocytic epithelium arranged in a double-layered pattern, with mitochondrial antigens strongly staining the luminal oncocytic cells. Cytokeratin 7 expression in Warthin tumors was predominantly luminal. In contrast, Group B showed glandular and cystic structures with diffuse mitochondrial antigen and cytokeratin 7 positivity. Immunohistochemical analysis revealed significant differences, with Warthin tumors showing distinct double-layered epithelial structures, and mucoepidermoid carcinomas displaying diffuse staining patterns. CONCLUSION: Distinct immunohistochemical profiles, including mitochondrial antigen and cytokeratin 7 expression, along with morphological differences, support the classification of Group A as metaplastic Warthin tumors and Group B as Warthin-like variants of mucoepidermoid carcinoma. These findings highlight the importance of molecular and immunohistochemical analyses for accurate classification of these tumors.