Upper respiratory tract tumors in Cpb:WU (Wistar random) rats.

A survey is given of upper respiratory tract tumors in Cpb:WU (Wistar random) rats. Data were collected from ten 24- to 30-month toxicity/carcinogenicity studies and from one 12-month study. Nasal tumors may lead to dyspnea, mouth breathing, and nasal discharge. These clinical signs mainly occurred in rats bearing squamous cell carcinomas. The large nasal tumors were often osteolytic, they invaded the subcutis over the premaxilla, resulting in swellings on the back of the nose, and extended into the brain. The incidence of nasal tumors in untreated male controls was 1.1% (7/661), the tumors invariably being squamous cell carcinomas. There were no nasal tumors found in untreated female controls. The type of compound-induced nasal tumor most frequently observed was adenocarcinoma (of the olfactory epithelium) followed, in order of decreasing incidence, by squamous cell carcinoma, carcinoma in situ, polypoid adenoma, Schwannoma, and carcinosarcoma. It was proposed that adenocarcinomas of the olfactory epithe...