Spontaneous renal neoplasms in rats.

Spontaneous renal neoplasms in the rat are uncommon. This paper presents the incidence and histopathological features of various long-term developing renal tumors observed in control rats from 17 carcinogenicity studies (1340 males and 1329 females) in Sprague-Dawley rats and 10 carcinogenicity studies (530 males and 530 females) in Fischer-344 (F-344) rats. Renal cell adenoma (0.08% in Sprague-Dawley and 0.28% in F-344), lipoma/liposarcoma (0.37% in Sprague-Dawley and 0.75% in F-344) and transitional cell carcinoma (0.07% in Sprague-Dawley and 0.09% in F-344) were observed in both Sprague-Dawley (0.49%) and F-344 (1.13%) rats. Pulmonary metastasis was observed from one case of transitional cell carcinoma. Renal cell carcinoma with metastasis to the lung and liver was seen in one F-344 rat. In addition, transitional cell papilloma and nephroblastomas were also observed in Sprague-Dawley rats. Metastases from nephroblastoma were seen in the lungs and renal lymph node in two cases. In both rat strains, the tumor incidence was higher in males than in females.