Ultrastructural Study on Experimental Lingual Carcinogenesis in the Hamster. II. Ultrastructural Study of Premalignant Lesions with an Emphasis on Abnormal Keratinization

An ultrastructural study of hamster lingual epithelium after the application of 9, 10-dimethy1-1, 2- benzanthracene (DMBA) was performed, with an emphasis on abnormal keratinization. In the initial stages, no sign of abnormal keratinization was seen. In the stages of diffuse and papillomatous epithelial proliferation, dilatation of intercellular spaces with a decrease in the number of desmosomes was seen. Nuclear changes associated with the increase in the number of ribosomes in the cytoplasm were also observed. These features were most conspicuous in papillomas. Abnormal keratinization such as hyper-keratosis, parakeratosis, acantholysis and dyskeratosis was noted. In the areas of diffuse epithelial proliferation, hyperkeratosis was well observed, while in papillomas parakeratosis and dyskeratosis were predominant. Two types of dyskeratosis were noticed ; an aggregation of tonofibrils around the nucleus like the "crown of thorn-like pattern" reported by Setala et al., individual cell keratinization accompanied with acantholysis. The cell membrane of the latter dyskeratotic cell was always thickened. In papil-lomas, an increase in the number of kerationosomes was seen, but they were diffusely distributed through-out the cytoplasm. On the other hand, the number of keratohyalin granules in the cells of papillomas was markedly reduced and the inner structure of them was greatly simplified. These results suggested that the disturbance of maturation in the keratinocytes occurred in papillomas