Aims A recent review of archived sections from early experiments in rats showed neoplasias exhibiting serrated configurations. The aim was to assess the frequency of serrated neoplasias in the colon and small intestine of carcinogen-treated rats.

Methods While reviewing archival sections from early experiments in Sprague-Dawley (SD) and Fisher-344 (F-344) rats, we recently detected colonic and intestinal traditional serrated adenomas (displaying serrated or microtubular patterns) and serrated carcinomas. SD rats were injected 1,2-dimethylhydrazine (DMH) for 27 weeks whereas F-344 rats were fed with a pyrolysate (GLU-1) for 24 months. Filed sections from 358 colonic and small intestinal neoplasias were re-evaluated.

Results DMH-treated SD rats had 215 colonic neoplasias (1.4% were serrated adenomas, 7.9% microtubular adenomas, 2.8% serrated carcinomas and 2.8% microtubular carcinomas). GLU1-treated F-344 rats had 53 colonic neoplasias (1.9% were serrated adenomas and 20.8% microtubular adenomas), and 89 small intestinal neoplasias (1.1% were serrated adenomas, 42.7% microtubular adenomas and 6.7%, microtubular carcinomas).

Conclusions DMH/SD-rats develop serrated and microtubular adenomas and carcinomas in the colon, whereas GLU1/F-344 rats develop microtubular adenomas in the colon and microtubular adenomas and carcinomas in the small intestine. The two rat-settings emerge as suitable models to study the molecular attributes of serrated and microtubular neoplasias under the standard conditions of the laboratory. This study is the first showing that a substantial number of serrated and particularly microtubular adenomas and carcinomas develop in the colon and small intestine of experimental rats. Importantly, serrated and microtubular neoplasias in rats recreate the histology of duodenal and colonic traditional serrated neoplasias in human beings.