Duration of ENNG administration and its effect on histological differentiation of experimental gastric cancer.

An experimental trial in the induction of canine gastric cancers was conducted to study the relationship between the histological differentiation of adenocarcinoma and the duration of administration of the carcinogen, N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG). Twenty-three adult Beagle dogs were divided into three groups according to the duration of administration. Over 3 months administration, the total dose of ENNG per animal was 5.85 g, and only signet ring cell carcinomas and poorly differentiated adenocarcinomas were induced in the antral mucosa of the stomach in 5 of 10 recipients. During 6 and 9 months administration, the total doses per animal were 11.70 g and 17.55 g, well differentiated adenocarcinomas were observed in 12 of 13 animals and they coexisted with poorly differentiated adenocarcinomas and/or signet ring cell carcinomas. Atrophic hyperplastic gastritis and hyperplastic polyps were seen in the same stomach. The results of this study suggest that a greater amount of carcinogen, i.e., a higher total dose, is required for the development of well differentiated adenocarcinoma than for inducing poorly differentiated adenocarcinoma and signet ring cell carcinoma.