Expression of Membrane-Bound Mucins and p63 in Distinguishing Mucoepidermoid Carcinoma from Papillary Cystadenoma

The aim of this study was to compare the immunoexpression of epithelial mucins (MUCs) in salivary duct cysts, papillary cystadenomas, and mucoepidermoid carcinomas and to evaluate if any of these markers could be useful for differentiating between mucoepidermoid carcinoma and papillary cystadenoma. We also sought to validate the p63 expression pattern found to differentiate between mucoepidermoid carcinoma and papillary cystadenoma. Immunoexpression of MUC1, MUC2, MUC4, MUC7, and p63 was studied and quantified in 22 mucoepidermoid carcinomas, 12 papillary cystadenomas, and 3 salivary duct cysts. The immunohistochemical evaluation was collectively performed by 3 oral pathologists. Scores and trends in proportions were assessed using the nonparametric Wilcoxon-Mann-Whitney rank sum test. Mucoepidermoid carcinomas, papillary cystadenomas, and salivary duct cysts demonstrated variable MUC expression patterns. All tumors were positive for p63 immunoexpression with p63 labeling in salivary duct cysts and papillary cystadenomas (15/15) limited to the basal layers of the cystic spaces, whereas in mucoepidermoid carcinomas (22/22) the p63 labeling extended throughout the suprabasal layers (p < 0.001). This study adds more confirmatory data to validate that the reactivity pattern of p63 protein can be used in distinguishing between papillary cystadenoma and low-grade mucoepidermoid carcinoma. Although positive reactivity in a tumor with MUC1 and MUC4 was inconclusive, negative reactivity suggests the diagnosis of a benign PC or SDC.