Reevaluation of Salivary Lymphadenoma: A Subgroup Identified as Warthin-like Mucoepidermoid Carcinoma Following Molecular Investigation for MAML2 Rearrangement.

Context.—: Both salivary lymphadenomas (LADs) and Warthin-like mucoepidermoid carcinoma (MEC) contain components of epithelium and lymphoid stroma and their differential diagnosis can be difficult on the basis of morphology alone.
Objective.—: To clarify whether Warthin-like MEC was diagnosed as a LAD, and to compare their clinicopathologic features.
Design.—: A total of 16 LAD cases were analyzed for MAML2 rearrangement by using fluorescence in situ hybridization, and the clinical, histologic, immunohistochemical, and prognostic features were compared between MAML2 rearrangement-positive and MAML2 rearrangement-negative groups.
Results.—: Among the 16 cases investigated, 9 harbored a MAML2 rearrangement and were reclassified as Warthin-like MEC. The remaining 7 cases were classified as LADs with 1 nonsebaceous and 6 sebaceous cases. The patients with Warthin-like MEC had a wider age range (10-75 years) than the patients with LADs (36-68 years). Histologically, 2 of the 9 Warthin-like MECs (22.2%) showed focal invasion, whereas all the LADs had complete capsules. Warthin-like MECs exhibited a diverse epithelial cell morphology, including basaloid, glandular, cuboidal, epidermoid, with mucinous cells, although these cytologic features were seen only focally in some cases. Nonsebaceous LAD was composed of basaloid and glandular epithelial cells predominantly. In sebaceous LAD, the epithelial cells were composed of basaloid and large foamy sebaceous cells. In all cases, the stroma was composed mainly of lymphocytes accompanied by lymphoid follicles, although plasma cell infiltration could be much heavier in Warthin-like MEC. All the patients had a good outcome after a longer follow-up (3-166 months).
Conclusions.—: Warthin-like MEC can be misdiagnosed as a LAD owing to overlap in clinicopathologic features of the 2 entities. Careful histologic evaluation and detection of MAML2 rearrangement can facilitate their differential diagnosis.