The significance of mucinous metaplasia in Warthin tumor: a frequent occurrence and potential pitfall

• Published in: Human pathology 2020-05, Vol.99, p.13-26
• Main Authors: Zhang, Xiaoming, Baloch, Zubair W., Cooper, Kumarasen, Zhang, Paul J., Puthiyaveettil, Raghunath, LiVolsi, Virginia A.
• Format: Article
• Language: English
• Subjects: Cysts; Gender differences; MAML2 rearrangement; Morphology; Mucinous metaplasia; Patients; Squamous metaplasia; Statistical analysis; Tumors; Warthin tumor; Warthin-like mucoepidermoid carcinoma
• ISSN: 0046-8177; 1532-8392
• DOI: 10.1016/j.humpath.2020.03.008

Mucinous metaplasia in Warthin tumor (WT) is a recognized phenomenon. Nevertheless, its presence can create a diagnostic challenge in the distinction from the newly proposed variant of mucoepidermoid carcinoma (MEC), Warthin-like MEC. In this study, we evaluated the significance and diagnostic relevance of mucinous metaplasia in WTs. A total of 30 WTs diagnosed based on resection specimens formed the basis of this retrospective study. Mucicarmine staining was performed to identify mucinous metaplasia, and fluorescence in situ hybridization (FISH) analysis was used to detect MAML2 gene rearrangement. After review, one MAML2 rearranged case was reclassified as Warthin-like MEC as the classic bilayered epithelium in WT was not identified. The diagnosis of WT was confirmed in the remaining 29 cases. Mucinous metaplasia was encountered in 24 WTs (83%), with 14% (4/29) having an abundant amount. We found that mucinous metaplasia correlated with tumor size (p  0.05). The MAML2 FISH analyses performed in 18 WTs with variable amounts of mucinous metaplasia were negative for rearrangement. In conclusion, mucinous metaplasia is fairly common in WTs and shows a significant correlation with tumor size. Therefore, caution should be taken to avoid overinterpretation of WT with mucinous metaplasia as MEC in cases showing the classic bilayered oncocytic lining epithelium.