Hormones, Breast Disorders, and Lactation

The breast is an organ, equal and symmetrical, of the human body. It develops, grows, acquires functions, and involutes according to the stage of life: puberty, pregnancy, lactation, and menopause. These modifications are induced by the hormonal variations that a woman experiences during the course of her life. Besides the normal evolution of the breast, hormones are responsible for many breast disorders, be them benign or malignant. The term benign breast disease is used to describe a wide variety of mammary clinical entities. Benign breast diseases are often referred to as para-physiological conditions in normal breast development and their prevalence peaks during the first four decades of the woman’s life. Hormonal dysregulations are thought to play a key role in the development of such disorders. Similarly, endogenous and exogenous hormonal modifications are listed as major risk factors for the development of breast malignancies: the link between sex hormones and breast tumors has long been known and confirmed in experimental biological models and epidemiological observations. The incidence curve of breast cancer grows with advancing age but plateaus over the years after menopause, in parallel with the cessation of ovarian hormone production. At this stage of life, concerns have been raised over the possible deleterious effect of hormonal replacement therapy (HRT) on breast benign diseases and breast cancer risk since the results of the WHI were published in 2001. The same issues are reported in literature for the previous consumption of combined oral contraceptives (OCs). Beginning from normal breast development, physiology, and pathology, the effect of OCs and HRT on breast benign disease and on the risk of breast cancer will be the subject of this chapter.