Clinicopathological practice in the differential diagnosis of mucoepidermoid carcinoma from neoplasms with mucinous component

Background:The differential diagnosis of mucoepidermoid carcinoma(MEC)from neoplasm undergoing mucinous features brings more pitfalls to pathologists.Combining specific MAML2 gene rearrangement and histological characteristics may be the solution.Methods:Twenty-five tumors with mucinous components were selected for differential diagnosis of MEC.All the cases were detected for MAML2 gene rearrangement.The cases diagnosed as MEC were classified into four variants:classic,oncocytic,Warthin-like,and nonclassified,and they were graded using the Brandwein system.The histological characteristics of non-MECs were summarized for differential diagnosis.Univariate survival analysis was performed on MECs.Results:There were 16 MECs;62.5%were MAML2 rearranged.For the low-,intermediate-,and high-grade MECs,the rate of rearrangement was 83.3%,100%,and 28.6%,respectively.Both the oncocytic and Warthinlike MECs were MAML2 rearranged.For the classic and nonclassified MECs without MAML2 rearrangement,non-keratinized squamoid cells and distinctive mucinous cells were essential diagnostic criteria.On survival analysis,all the disease progression occurred in high-grade MECs(p=0.038).Nine cases were diagnosed as non-MECs:pleomorphic adenoma with mucinous metaplasia showed no ex-capsular involvement;metaplastic Warthin tumor appeared with overt keratinization and residual oncocytic bilayered epithelium;mix squamous cell and glandular papilloma showed an endobronchial papillary growing pattern;adenosquamous carcinoma was accompanied by squamous carcinoma in situ of the overlying mucosa.All the non-MECs were negative for MAML2 rearrangement.Conclusion:The application of combining MAML2 rearrangement and histological characteristics is helpful in the differential diagnosis between MEC and other tumors with mucinous components.