Sequential morphological studies of the esophageal carcinoma of rats induced by N-methyl-N-amylnitrosamine.

N-Methyl-N-amylnitrosamine was given to male Wistar rats in the drinking water at a concentration of 0.003% for 8 weeks. Three rats were autopsied weekly from the first to the 25th week. The stages of hyperplasia, dysplasia and squamous cell carcinoma in the esophagus were chronologically observed. Hyperplasia and dysplasia were found by the 6th week and continuously observed until the end of the experiment. Early squamous cell carcinomas were found in the 13th week. They showed endophytic or exophytic growths. Histologically, the endophytic growths were well-differentiated squamous cell carcinomas and the exophytic growths were poorly-differentiated. Advanced carcinomas were first found in the 15th week and were almost well-differentiated. Carcinomas were not found in papillomas. The incidence of carcinomas increased with time, being 9 out of 15 rats (60%) in the final 21st through 25th weeks. Lymph node metastasis was found in one rat, killed at the 24th week.