Fetal cells are probably actively migrating from peripheral blood into the tumor tissue where they are preferentially settled in the tumor stroma and their concentration decreases as they get closer to the healthy breast tissue. There are two suggested mechanisms by which the fetal cells could have the positive effect on the breast cancer prognosis. First mechanism suggests that fetal cells only oversee cancer cells and they attract components of the immune system if needed. The second option is that the down-regulation of the immune system induced by the presence of fetal cells could ultimately lead to cancer prevention, because women in whom FMC is present produce lower concentrations of inflammatory mediators, which may lead to the development of neoplastic tissue.