Induction of duodenal-tumors and thymomas in Fischer rats by continuous oral administration of 1-propyl-1-nitrosourea.

Male and female F344/DuCrj rats were given 400 ppm solution of 1-propyl-1-nitrosourea continuously in their drinking water. The incidence of digestive tract tumors was as high as 32/36 (89%) and 33/39 (85%) in male and female rats, respectively. Among these, duodenal tumors were induced most frequently, and most of them were adenocarcinoma followed by adenomas and hemangiogenic tumors. Thymomas were found in 27 (75%) males and 14 (36%) females. The lymphocytic type thymoma was the most frequent, and epithelial or mixed types were found only in 8 females. Other tumors induced were mainly in the ear ducts and lung, and the incidence was less than 13%.