[Pathologic changes of spontaneous tumors in Sprague-Dawley and Wistar rats]

Objective: To investigate the spontaneous neoplastic lesions and their incidences in Sprague-Dawley (SD) and Wistar rats, and to accumulate background data for carcinogenicity studies. Methods: One hundred and eighty SD rats and 240 Wistar rats (4-week old) , half in each sex, were used in this study. The rats were housed routinely under specific pathogen-free environment and euthanized after 104 weeks. Histopathological examination was undertaken for all animals including deaths and scheduled euthanasia. The types and incidences of spontaneous tumors were gathered statistically. Results: Total 411 rats (176 SD rats and 235 Wistar rats) were examined in this study. The total tumor incidence of the 411 rats was 57.7%(237/411). The total tumor incidence in SD rats was 55.7%(98/176), benign tumor incidence was 48.9%(86/176) and malignant tumor incidence was 15.9%(28/176). The total tumor incidence in Wistar rats was 59.1%(139/235), benign tumor incidence was 51.5%(121/235) and malignant tumor incidence was 14.5%(34/235). The main benign tumors were pituitary adenoma (23.3% in SD rats, 12.3% in Wistar rats), breast fibroadenoma (21.3% in SD rats, 12.9% in Wistar rats) and breast adenoma (16.9% in SD rats, 9.5% in Wistar rats) in females; testis Leydig cell tumor (0 in SD rats, 14.3% in Wistar rats) in males. The main malignant tumors were breast carcinoma (10.1% in SD rats, 3.4% in Wistar rats) and uterine leiomyosarcoma (0 in SD rats, 2.6% in Wistar rats) in females; squamous cell carcinoma of skin (2.3% in SD rats, 0.9% in Wistar rats); subcutaneous fibrosarcoma (1.1% in SD rats, 2.1% in Wistar rats); brain malignant glioma (1.1% in SD rats, 1.7% in Wistar rats). Conclusions: In the study, a high incidence of spontaneous tumors is reported in both SD and Wistar rats housed for 2 years. The incidence of benign tumors is higher than that of malignant rumors. The benign tumors mainly are pituitary adenoma, breast fibroadenoma and breast adenoma in females, and testis Leydig cell tumor in males. The malignant tumors mainly are breast carcinoma and some soft tissue sarcomas. The results of the study enrich the data of spontaneous tumor in SD and Wisar rats and provide background data for carcinogenicity studies for new drugs.