[Risk of breast cancer related to pregnancy]. / Risque de cancer du sein lié à la grossesse.

After a pregnancy, there is a transitory increase in the risk of breast cancer. During the pregnancy, the number of mammary epithelial cells increases massively. This increase seems partly due to the expansion of stem cells and proliferating intermediate cells. This proliferation of epithelial cells is accompanied by angiogenesis and by recruitment of stromal cells, as well as changes of the extracellular matrix. During any pregnancy, there is cell trafficking between mother and foetus. Hematopoietic or mesenchymal foetal stem cells are transferred in maternal circulation and could be used by the tumor as support cells and take part in the tumoral development. The study of the mechanisms of this specific oncogenesis may help to develop chemoprevention strategies.