Sclerosing mucoepidermoid carcinoma of the salivary glands: report of three cases with special concern to the counterpart accompanied by eosinophilia

Sclerosing mucoepidermoid carcinoma (SMC) is described as a “sclerosing variant” of mucoepidermoid carcinoma, and it is characterized by dense fibrosis and sclerosis of the stroma. SMC with eosinophilia (SMCE) is another and more rare subtype characterized by eosinophilia in addition to the sclerotic stroma common to SMC. However, unlike SMC, SMCE is not listed in the current 4th edition of WHO classification. Here, we describe three cases: one SMC in the parotid gland, one SMCE in the submandibular gland and one SMCE in the minor salivary gland of the oral cavity. The patients included a 71-year-old Japanese male, a 74-year-old Japanese female, and an 81-year-old Japanese female. They each complained of mass formation and underwent surgical resection. Histologically, the tumors mainly consisted of squamous cells with scarce keratinization that formed irregular large and small nests along with cystic structures containing mucous cells against the background of sclerotic stroma. One oral SMCE showed fine nesting and trabecular invasion. The two SMCEs included dense aggregates of eosinophils as well as more prominent lymphoid infiltration. Fluorescence in situ hybridization for MAML2 confirmed split signals in SMC, but not in SMCE.