Neoplastic lesions were observed in untreated aged Sprague Dawley (SD) rats throughout their lifespan starting at 5 weeks. Their mean survival times were 89 to 105 weeks of age. The total tumor incidences were 70 to 76.7% and 87 to 95.8% in males and females, respectively. The common neoplasmas were pituitary adenoma and adrenal pheochromocytoma in both sexes, testicular Leydig cell tumor in males and mammary gland tumors, thyroidal C-cell adenoma and uterine stromal polyp in females.

An intracranial epidermoid cyst was identified within the fourth ventricle of a male 10-month-old beagle dog. The cyst, which exhibited a multilocular structure, was lined by a stratified squamous epithelium and filled with desquamated keratin. In the region of the roof of the fourth ventricle, choroid plexus adherent to the cyst wall and secondary compression of the cerebellum were also seen.

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A malignant granulosa cell tumor and a benign granulosa/theca cell tumor were found in a 124-week-old Sprague-Dawaley female rat. These ovarian tumors were deemed to be estrogenically active because of the presence of severe adrenal peliosis. Pituitary prolactinoma and mammary adenocar cinoma were also found. Sex hormones were not measured, but the concomitant occurrence of ovarian, pituitary, and mammary tumors suggested that estrogen derived from ovarian tumors could have induced prolactinoma and that prolactin derived from the pituitary tumor could have been an important factor in producing the mammary adenocarcinoma.

No abstract