Incidence of Respiratory Metaplasia of the Nasal Gland Epithelium in Untreated F344 Rats and BDF1 Mice Subjected to Two-Year Carcinogenicity Studies

The incidence, distribution, and histopathology of respiratory metaplasia of the nasal gland epithelium were examined in F344 rats and BDF1 mice used as untreated control animals in 2-year carcinogenicity studies. Lesions were detected in almost all the male and female rats, while they were only detected in 67.8% and 46.6% of the male and female mice, respectively. In rats, most lesions were located in the septal and/or nasoturbinate subepithelial glands at the incisive papilla level, whereas the lesions varied in location and were histopathologically more severe in mice.