Incidence of neoplastic lesions in untreated Sprague-Dawley rats (1340 males and 1329 females) used as controls in 17 carcinogenicity studies are tabulated and evaluated. In male rats, the most common neoplasms were benign pheochromocytomas and keratoacanthomas (4.0% in each case) followed by pancreatic islet cell adenomas (3.7%), thyroid parafollicular cell adenomas (3.6%), fibromas and squamous cell papillomas of the skin and hepatocellular adenomas (2.0% in each), malignant lymphoma lymphocytic (1.9%), histiocytic sarcomas (1.4%), and adrenal cortical adenomas (1.2%). In female rats, the most common neoplasms were of mammary gland origin (31.3%: fibroadenoma 19.0%, adenocarcinomas 8.8%, and adenomas 3.5%) followed by thyroid parafollicular cell adenomas (2.9%), uterine endometrial stromal polyps (2.6%), adrenal cortical adenomas (1.9%), malignant lymphoma lymphocytic (1.6%), fibromas in the skin (1.3%), and pancreatic islet cell adenoma (1.1%). Metastases were observed from pheochromocytomas, hepatocellular carcinomas, nephroblastomas, renal pelvis transitional cell carcinoma, interstitial cell tumor and seminoma of the testes, Zymbal's gland adenocarcinomas, and mammary adenocarcinomas.
Hematopoietic neoplasms in the rodent may be classified into lymphoid or nonlymphoid neoplasms. Lymphoid neoplasms include the following morphologic types: follicular center cell, lymphoblast (lymphocytic), immunoblast, plasma cell, and large granular lymphocyte (LGL
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.
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