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Benign lymphoepithelial lesions of the salivary glands associated with Sjögren's syndrome are characterized by extensive infiltration of lymphoid cells, atrophy of acini and the presence of so-called epimyoepithelial islands. This report describes ultrastructural and three-dimensional reconstructive studies of epimyoepithelial islands performed at Tokyo Women's Medical College. Ultrastructural examination showed that these islands are composed mainly of epithelial cells containing intermediate filaments and/or tonofilament bundles, scattered lymphocytes and plasma cells. Myoepithelium-like cells containing myofilaments were sometimes found in the peripheral portion of the myoepithelial islands. Also, mitotic figures were rarely found in these islands. Three-dimensional reconstructive study revealed that the epimyoepithelial islands are not isolated cell clusters but are continuous hypertrophic duct-like structures. These results suggest that the epimyoepithelial islands are derived from proliferating duct epithelial cells, especially those of large peripheral ducts.

A case of carcinoma ex pleomorphic adenoma arising in the soft palate is reported. The tumour presented had enlarged gradually over 10 years and finally occupied the oral cavity. The patient was admitted to our hospital due to disturbance of her speech and swallowing, and a sudden haemorrhage from the tumour. The initial pathological diagnosis by open biopsy was benign pleomorphic adenoma. After total resection, histological examination revealed that the tumour was composed partly of benign pleomorphic adenoma and partly of an adenocarcinomatous component. The carcinoma cells with prominent nucleoli were spheroid or polygonal in shape, and frequently formed ductal structures with areas of necrosis. Mitoses were also found. These findings showed that this tumour was a secondary carcinoma which had developed in a preexisting pleomorphic adenoma.