Induction of carcinoma of the large intestine in guinea pigs by intratectal instillation of N-methyl-N-nitrosourea.

Intrarectal administration of 0.5 ml of a 0.25 percent solution of N-methyl-N-nitrosourea twice seekly for 42 weeks to female inbred strain-2 guinea pigs induced large-bowel adenocarcinomas in 9 of 10 animals in 38-56 weeks. Controls did not show cancer. The lesions were infiltrative or constrictive, which distinguished them from chemically induced large-bowel cancers of rats and mice.