Spontaneous lesions in virgin and retired breeder BALB/c and C57BL/6 mice.

Prevalences of neoplastic and nonneoplastic lesions were reported for 3,000 virgin and 800 retired breeder BALB/c and C57BL/6 mice, untreated and of both sexes. The most common nonneoplastic lesions in the BALB/c mice were: hepatic fatty metamorphosis, uterine hemosiderosis and mineralization, testicular atrophy, ovarian cysts, and adrenal subcapsular spindle cell hyperplasia. The most common neoplasms in the BALB/c mice were: pulmonary tumors, hepatocellular neoplasms, Harderian adenomas, and uterine polyps. Common nonneoplastic lesions in the C57BL/6 mice were: pulmonary lymphoid accumulations, hepatic fatty metamorphosis, multifocal aggregates of mononuclear cells in the liver, proteinaceous renal casts, uterine hemosiderosis, endometrial cystic hyperplasia, ovarian atrophy, ovarian cysts, and pituitary cysts. The most common neoplasms in the C57BL/6 mice were angiosarcomas and pituitary adenomas. Hematopoietic tumors were common in both strains.