Each year, 50,000 new cases of breast cancer are diagnosed in France and 11,000 women die from it. After a sharp increase, partly explained by the screening program implementation, the incidence rate has decreased for few years. Since the 2000s, the mortality rate has been declining steadily. Many risk factors for breast cancer are known or suspected. Endogenous hormonal factors (age at menarche, menopause, first pregnancy, lactation, number of children) and exogenous (hormone replacement therapy, contraception...) are known risk factors. The lifestyle (weight, diet, physical activity, night work), the family past history as well as environmental pollution may also play a role in breast cancer development. Even if all these factors have individually only a low impact on the occurrence of breast cancer, their effects are additive. However, many patients who will develop breast cancer do not present currently known risk factors.