Pathology of esophageal neoplasms and associated proliferative lesions induced in rats by N-methyl-N-benzylnitrosamine.

Multiple squamous cell neoplasms of the esophagus were induced in 24 inbred F344 rats by sc injection of N-methyl-N-benzylnitrosamine at a dose level of 2.5 mg/kg weekly for 20 weeks. All of these rats also developed papillomas, 67% developed pedunculated papillary carcinomas, and 63% developed carcinomas that invaded the wall. Of 191 total neoplasms, 66% were papillomas, 17% were papillary carcinomas, and 17% were carcinomas that invaded the wall. The neoplasms were well differentiated with various degrees of keratinization. Anaplastic areas were found in most lesions, but were more common in carcinomas. Neoplasms that invaded the wall were sessile, with prominent intraluminal growth, or infiltrating, with predominant intramural growth. Penetration through the wall was observed, but neither metastases nor invasion of adjacent tissues was found. In addition to neoplasms, atypical endophytic proliferation of basal and spinous cells was observed in some of these rats. Proliferative or neoplastic changes were not observed outside the upper gastrointestinal tract.