Diagnosis:
Mucoepidermoid carcinoma
• Mucoepidermoid carcinoma (MEC) consists of irregular cellular nests that show invasive growth into adjacent nonneoplastic tissue. The lesion contains variable proportions of three cell types: epidermoid/squamoid cells, goblet cells, and intermediate/basaloid cells. Squamous metaplasia and keratinization may be present. Mitotic activity ranges from rare to brisk.
• The degree of differentiation of MEC is directly proportional to the amount of goblet cells, and inversely proportional to the amount of intermediate/basaloid cells. Well differentiated cases show abundant goblet cells, whereas goblet cells are rare in poorly differentiated tumors.
• Carcinoma ex pleomorphic adenoma usually manifests as poorly differentiated adenocarcinoma, which may be histologically similar to poorly differentiated MEC. In carcinoma ex pleomorphic adenoma, adequate sampling should demonstrate a relationship between the carcinoma and a preexisting pleomorphic adenoma. Likewise, some cases of poorly differentiated MEC may require generous sampling in order to demonstrate recognizable areas of a better differentiated tumor.
• Goblet cells are not a feature of polymorphous low-grade adenocarcinoma (PLGA) or adenoid cystic carcinoma.
• Acinic cell carcinoma may contain cells with intracytoplasmic vacuoles, which may show positive periodic acid-Schiff (PAS) staining. These vacuoles contain secretory granules rather than mucin, and are not stained by mucicarmine.
