ABSTRACT

It has long been appreciated that early pregnancy acts as a critical protective factor for breast cancer both in human epidemiologic studies as well as rodent model systems with exogenous carcinogens. In this paper, hormonal effects of exogenous hormones as well as pregnancy on breast differentiation are explored. It is shown that pregnancy differentiates the terminal end buds into secretory units which are substantially more resistant to carcinogenic effects. Furthermore, pregnancy-induced morphogenetic events persisted indefinitely following parturition, providing lifetime risk reduction.