Apoptosis in mammary gland and cancer

Homeostasis in normal tissue is regulated by a balance between proliferativ e activity and cell loss by apoptosis. Apoptosis is a physiological mechani sm of cell loss that depends on both pre-existing proteins and de novo prot ein synthesis, and the process of apoptosis is integral to normal mammary g land development and in many diseases, including breast cancer. The mammary gland is one of the few organ systems in mammals that completes its morpho logic development postnatally during two discrete physiologic states, puber ty and pregnancy. The susceptibility of the mammary gland to tumorigenesis is influenced by its normal development, particularly during stages of pube rty and pregnancy that are characterized by marked alterations in breast ce ll proliferation and differentiation. Numerous epidemiologic studies have s uggested that specific details in the development of the mammary gland play a critical role in breast cancer risk. Mammary gland development is charac terized by dynamic changes in the expression profiles of Bcl-2 family membe rs. The expression of Bcl-2 family proteins in breast cancer is also influe nced by estradiol and by progestin, Since the ratio of proapoptotic to anti apoptotic proteins determines apoptosis or cell survival, hormone levels ma y have important implications in the therapeutic prevention of breast cance r.