Tumour-simulating squamous cell metaplasia (SCM) in necrotic areas of salivary gland tumours.

Squamous cell metaplasia (SCM) adjacent to necrotic areas of salivary gland tumours must be distinguished from other types of SCM (focal SCM in the excretory ducts of salivary glands; necrotizing sialometaplasia; focal SCM within salivary gland tumours) in respect to the tissue structure. Based on the high cellular proliferation, arcade- or cord-like pseudoneoplastic SCM develops with stellate extension in the surrounding tissue and focal inclusion of goblet cell metaplasia. This proliferative SCM resembles the cellular demarcation of radicular dental cysts. In the Salivary Gland Register 8 cases of tumor-simulating SCM could be analysed which clinically and morphologically were suspect of squamous cell or mucoepidermoid carcinoma. Five cases were localized in the parotid gland, 2 cases in the submandibular gland and 1 case in the palatinal glands. Tumour-simulating SCM was developed in pleomorphic adenomas (5 cases) and in multifocal adenomatous oncocytic hyperplasia (3 cases).