Appearance of ear tumors in Sprague-Dawley rats treated with 1,2-dimethylhydrazine when used as a model for colonic carcinogenesis.

One of the models of colon carcinogenesis in rats is produced by s.c. injections of 1,2-dimethylhydrazine (DMH). This specific colon carcinogen provokes other tumors in the rat, notably intestinal tumors. Ear tumors are just marginally mentioned in the literature. We have studied the appearance and histologic characteristics of ear tumors produced by 19 s.c. injections of 21 mg/kg of DMH in 18 Sprague-Dawley rats: 15 tumors appeared in 13 ears of 10 rats (55% of the animals). Simultaneously there were 23 colonic tumors: four (26.6%) of the tumors were carcinomas, 10 (66.6%) papillomas and one (6.6%) pseudoepitheliomatous hyperplasia. We conclude that ear tumors induced by DMH appear in 55% of the rats and that it is not possible to distinguish macroscopically in terms of size and aspect between benign and malignant lesions.