Pathology of aging female SENCAR mice used as controls in skin two-stage carcinogenesis studies.

The pathology of 60 aged female SENCAR mice used as acetone controls in skin painting studies was studied. Fifty percent of the mice survived past 96 weeks of age. The major contributing causes of death identified in 42 mice were glomerulonephritis (8 mice), histiocytic sarcoma (7 mice), and other tumors (8 mice). Glomerulonephritis was found in the majority of mice and was associated with thymic hyperplasia, focal vasculitis, and lymphoid hyperplasia. Necropsy of 58 mice surviving past 50 weeks of age revealed that 41 had an average of 1.36 tumors per mouse. The most common tumors included histiocytic sarcoma (13 mice), pulmonary adenoma or adenocarcinoma (11 mice), mammary tumors (11 mice), follicular center cell lymphoma (4 mice), and hepatocellular adenoma (4 mice). The 13 histiocytic sarcomas appeared to arise in the uterus and metastasized to liver (9 mice), lung (4 mice), kidney (3 mice), and other tissues. Lung tumors were of the solid and papillary types, and tumor cells frequently contained surfactant apoprotein (SAP) but did not contain Clara cell antigens, suggesting their origin from alveolar Type II cells. A variety of nonneoplastic lesions, similar to those observed in other mouse strains, were seen in other tissues of these mice. Amyloid-like material was seen only in nasal turbinates and thyroid gland. In a group of 28 mice exposed to 12-O-tetradecanoylphorbol-13-acetate (TPA) for up to 88 weeks, as a control for other treatment groups, 7 (25%) had papillomas and 5 (17.8%) had squamous cell carcinomas of the skin at necropsy, although many other induced papillomas regressed during the study.