Age-related changes in mammary gland DNA synthesis as a limiting factor for mammary tumorigenesis in rats and its implication for human breast cancer.

Most age-related changes in carcinogen-induced mammary tumorigenesis are due to changes in the dynamic aspects of normal mammary glands. The decreased risk of human breast cancer associated with early pregnancy can also be explained by such changes. There are other factors that influence age-related changes in mammary tumorigenesis; however, their effects would be nullified by higher levels of carcinogens or promoters.