Early Gastric Cancer Induced by N‐Ethyl‐N′‐nitro‐N‐nitrosoguanidine in a Cynomolgus Monkey Six Years after Initial Diagnosis of the Lesion

A signet ring cell carcinoma in the gastric antrum of a Cynomolgus monkey induced by N‐ethyl‐N′‐nitro‐N‐nitrosoguanidine was sequentially studied by endoscopy, biopsy, and autopsy. The carcinoma was first detected on the angulus of the stomach at the 38th month as a slightly elevated lesion. Sixty‐one months later this tumor was found to be still in the “early”(intramucosal) stage. Another, independent, initial gastric cancer was also discovered. This is the first example of an induced gastric carcinoma remaining in the “early’stage during a six‐year follow‐up period after the initial histologic diagnosis.