Epidemiology of breast cancer: an environmental disease?

Breast cancer is the leading cancer site in women, both in the developed and the developing world. Incidence rates are increasing in many countries, although, in some, mortality may be stable or slightly decreasing. Geographical differences exist, with high rates of disease in North America, North Europe and Oceania, intermediate rates in South and Central America as well as South and East Europe, and low rates in Africa and Asia. Most of the literature reports that genetic inherited factors account for less than 5% of cases, although some authors advance higher figures, up to about 10%. Risk factors for breast cancer are related to the reproductive life of women: early menarche, nulliparity or late age at first birth, late menopause, diet and physical exercise, as well as hormonal factors, be they endogenous (high levels of free or not bound to SHBG estrogens) or exogenous (long-term use of oral contraceptives or menopausal hormone replacement). The present review does not aim to be exhaustive and fully comprehensive, or to present in detail domains currently well known and accepted by all. On the contrary, it modestly wishes to highlight potentially controversial conditions which could in the future be recognized as new risk factors.