Induction of digestive-tract tumors in F344 rats by continuous oral administration of N-butyl-N-nitrosourea.

Male and female F344/DuCrj rats were administered N-butyl-N-nitrosourea at a concentration of 400 ppm in their drinking water. By the 50th week of the experiment, the cumulative incidence of upper-digestive-tract tumors was as high as 35/39 (90%) and 34/39 (87%) in male and female rats, respectively. Among these, esophageal and forestomach tumors occurred most frequently. Except one female rat with fibroma, upper-digestive-tract neoplasms were of the epithelial type -- papilloma, squamous-cell carcinoma or adenocarcinoma. In female rats, vaginal tumors were induced in 16 (41%) animals. Ear-duct tumors and hematopoietic neoplasms were also induced in both sexes of rats, with incidence of less than 21%.