Concomitant Low-Grade Mucoepidermoid and Intraductal Carcinomas the Parotid Gland: Case Presentation with a Brief Review

The patient was a Japanese female and a former thyroid cancer patient. A computed tomography scan indicated a small mass in the right parotid gland about 14 years after therapy for thyroid cancer. Pleomorphic adenoma was suspected by contrast-enhanced magnetic resonance imaging. Three years later, when she was 60 years old, fine needle aspiration cytology failed to determine a diagnosis and superficial parotidectomy was performed. There have been no signs of recurrence or metastasis for about 2 years thereafter. Histological examination revealed two histological types of low-grade mucoepidermoid carcinoma and low-grade intraductal carcinoma coexisting within the parotid mass. Although closely located, the two types of carcinoma had not intermingled. The mucoepidermoid carcinoma formed multilocular cystic structures, in which mucous, intermediate, and non-keratinizing squamous cells were intermingled. Exclusively predominant intraductal growth in the intraductal carcinoma showed a combination of cribriform and papillary-cystic patterns and diffuse positive reaction for S100 protein. Fluorescence in situ hybridization demonstrated the mucoepidermoid carcinoma had split signals for the MAML2 gene but no split signals were detected for the MAML2 and ETV6 genes in the intraductal carcinoma. We discuss the histomorphological features and diagnostic problems of the present case and the literature is briefly reviewed.