Histopathology of Tumors of Canine Alimentary Tract Produced by N-Methyl-N'-nitro-N-nitrosoguanidine, With Particular Reference to Gastric Carcinomas

Four 90-day-old dogs were given 167 µg/ml solution of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) orally for 1 month and 83 µg/ml of solution for the following 14 months. All dogs developed adenocarcinomas, often multiple, of the stomach, the diagnosis of which was based entirely on the histologic appearance of the lesions. No metastases were found. Carcinomas developed most frequently in the cardiac portion along the greater curvature and in the antrum along the lesser curvature. In the greater curvature, all 4 dogs developed papillary and tubular adenocarcinomas, which were probably unrelated to previous ulceration of the mucosa. In the antrum, all 4 dogs developed papillary adenocarcinomas or adenocarcinomas with or without signet-ring cells. The muscularis mucosae was frequently replaced by fibrous tissue, which suggested marked tissue damage or ulceration of the mucosa before neoplastic growth developed, though the possibility of carcinoma developing in unulcerated mucosa still remained. The corpus mucosa of the ventral wall near the antrum was the site of carcinoma consisting predominantly of signet-ring cells, which appeared to originate in mucosa much less damaged by MNNG solution. Besides gastric adenocarcinomas, spindle cell sarcoma and hem,angioblastoma were found in the gastrointestinal tract. The histology of MNNG-induced gastric carcinomas is detailed and discussed mainly from the pathologic standpoint.