[Breastfeeding and breast cancer].

The objective of this review is to summarize the current knowledge about the impact of pregnancy and lactation on the risk of breast cancer and possibility of breastfeeding after breast cancer treatment. A Pubmed search was carried out for publications in English or French from 1974 through 2004, related to breast cancer, pregnancy and breastfeeding. There is a transient increase in risk of breast cancer in the first three to four years after pregnancy, whereas during lifetime, the risk seems lower than in nulliparity. Lactation reduced the risk for breast cancer. This protective effect seems greater for women who had extended periods of breastfeeding during their lifetime, particularly in case of BRCA1 mutation. Various physiopathological mechanisms are involved in the protective effect of breastfeeding: anovulation, cellular differentiation of the mammary cells and excretion in the milk of breast carcinogens. After breast cancer treatment, there is no evidence that breastfeeding increases the risk of breast cancer recurrence, nor that it carries any health risk to the newborn. Women previously treated for breast cancer and free of recurrence are allowed to breastfeed their children. Beneficial effects of breastfeeding for the mother and the newborn should lead physicians and midwives to encourage prolonged breastfeeding in their medical practice.