Squamous cell carcinoma arising in Warthin's tumor of the parotid gland. A light, electron microscopic, and immunohistochemical study.

The fourth recorded squamous cell carcinoma arising in a pre-existing Warthin's tumor is reported. A gradual transition was noted from the mitochondria-rich epithelium of benign portions of the tumor to organelle-poor cells forming the areas of squamous metaplasia and carcinoma. Bundles of intermediate filaments corresponding to immunoreactive keratin were demonstrated in all epithelial parts of the tumor and also in the epithelium of a benign Warthin's tumor that was studied in parallel.