Tumors of the upper digestive tract of ACI/N rats given N-propyl-N-nitrosourethan in the drinking water.

Three groups of ACI/N rats of both sexes were given 400, 200, or 100 ppm of N-propyl-N-nitrosourethan (PNUR) continuously in the drinking water. The incidence of tumors in the upper digestive tract was 100% in all 3 groups. These tumors were observed most frequently in the forestomach, followed by the esophagus, oral cavity, and pharynx. Histologically, all the tumors were papillomas or squamous cell carcinomas. A few tumors were detected in the small intestine and glandular stomach. The study on morphogenesis of squamous cell carcinomas arising from the upper digestive tract indicates that the majority of tumors of the esophagus and forestomach may pass through acanthosis or hyperkeratosis, leukokeratosis, and papilloma, and finally develop into invasive squamous cell carcinoma, but many carcinomas of the oral cavity and pharnyx, especially the tongue, may develop without passing through a papillomatous stage.