Glycogen-rich clear cell carcinoma in the tongue. A cytochemical and ultrastructural study.

An unusual epithelial neoplasm arising in the tongue of a 17 month-old-boy was studied by light and electron microscopy. By routine light microscopic examination, the tumor cells exhibited clear cytoplasm. Histochemical studies revealed the presence of large amounts of periodic acid-Schiff (PAS)-positive, diastase-labile material in the cytoplasm. Ultrastructurally, this material was identified as electron dense particles (20-35 nm diameter) of beta-glycogen. The epithelial nature of the tumor cells was suggested by the presence of intercellular junctions, segments of basal lamina, and well-developed Golgi complexes. Furthermore, the cells were often clustered and formed abnormal lumina with small microvillus projections. Several histologic features, such as lack of capsule, infiltration of muscle and invasion of blood vessel, indicated that this neoplasm was malignant. However, there was no recurrence or distant metastases more than 2.5 years after surgical excision, suggesting a low-grade malignancy. The glycogen-rich clear cell variant of adenocarcinoma is histogenetically derived from minor salivary glands like most of the glandular neoplasms in the oral cavity. Investigation of the literature on adult and childhood minor salivary gland neoplasms revealed that the glycogen-rich, clear-cell variant of adenocarcinoma has not previously been reported in the tongue.