[Impact of hormonal factors on breast cancer risk]

Breast cancer is the most common cancer in women. Women are exposed to various hormonal factors throughout their lives, which can impact their risk of breast cancer. Early menarche and late menopause are associated with an increased risk of breast cancer, particularly hormone-dependent cancers. Parity and breastfeeding, on the other hand, have a protective effect. Hormonal contraception, particularly combined contraception, slightly increases this risk during use. Hormone replacement therapy combining estrogen and progestin is associated with an increased risk, and to a lesser extent when treatment is combined with natural progesterone, or when it consists of estrogen therapy alone. Assisted reproductive technology is not associated with a significant increase in risk. These factors have a different influence depending on the tumour subtype.