Modifying factors in pancreatic carcinogenesis in the hamster model. I. Effect of protein-free diet fed during the early stages of carcinogenesis.

The role of protein in pancreatic carcinogenesis was examined in outbred Syrian golden hamsters treated with the pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine (BOP) and fed a purified protein-free diet (PPFD). The PPFD was fed for 28 days from 8 weeks of age; before and after animals were fed PPFD, they were given a commercial diet (CD). BOP was given before PPFD feeding (group 1) or at 18 days (group 2) and 28 days (group 3) from the beginning of the PPFD feeding. BOP-treated control hamsters (group 4) were pair-fed a purified control diet (PCD) instead of PPFD. All animals fed PPFD and PCD were returned to a CD for the rest of the experiment, which was terminated in each group 52 weeks after BOP treatment. The results showed a highly significant reduction of tumor incidence (P less than 0.0001) in hamsters that received PPFD, when compared to those fed PCD, regardless of the time of carcinogen administration during the dietary regimen. Hamsters treated with BOP at 18 days of PPFD (group 2) developed neither benign nor malignant pancreatic tumors. The inhibition of pancreatic neoplasms was not related to reduced calorie consumption, since this occurred in the BOP-treated hamsters that were pair-fed the PCD diet. The results indicated that both the initiation and promotion of pancreatic carcinogenesis with BOP in hamsters can be inhibited by lack of protein in the diet given for 4 weeks during the early stages of the neoplastic process.