Spontaneous tumors in SENCAR mice.

A total of 305 female and 36 male SENCAR mice in six different groups were observed for 540 to 875 days for tumors as well as nonneoplastic lesions. Three of these groups were observed for their lifespans. The 123 females and 36 males, observed for their lifespans (800 to 875 days) showed median survival times ranging from 730 to 745 days. The average peak body weights were 42.4 g for females and 50.0 g for males. In the animals observed for their lifespans, the total tumor incidence was 65.6% for females and 69.4% for males. Both sexes showed a high incidence of papillary tumors of the lung, 16 to 39%, which was independent of aging. Females showed a 5.1 to 21.0% incidence of mammary tumors, which increased with age. Males showed a high incidence of hyperplastic nodules of the liver, i.e., 12 of 36 animals. Other frequently occurring tumors were leukemia and papillomas of the forestomach.