Regression of polyploid carcinoma induced by N-methyl-N'-nitro-N-nitrosoguanidine in the stomach of a dog.

Polyploid carcinoma in the gastric antrum of a Beagle dog induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was sequentially studied by endoscopy and biopsy. Ulcer appeared on the angulus of the stomach at the 28th week and resulted in ulcer scar at the 42nd week. A new depression with atypical glands arose on the ulcer scar at the 69th week, developed elevated border at the 77th week, and progressed to a polyploid lesion at the 90th week. Well-differentiated adenocarcinoma in situ was found in the polyploid lesion at the 97th week. It gradually grew with nodular change of its surface. However, the carcinoma was ulcerated at the 126th week, became an elevated lesion with central depression at the 138th week, and finally regressed at the 154th week. At necropsy on the 202nd week, no carcinoma was found in the stomach.