Role of Progestins and Progesterone Receptors in Breast Cancer Biology

Progesterone is a major component in the regulation of normal female reproductive function. Its main physiologic role in the mammary gland is the lobular-alveolar development in preparation for milk secretion and suppression of milk protein synthesis prior to parturition (1). Its role in the proliferation of the normal mammary gland and in the initiation of breast cancer is the subject of controversy (for review, see ref. 2).