Breast cancer is the most common malignancy in women. Despite much progress in its  identification, advanced surgical techniques and chemotherapies, physicians have not been successful in the control and inhibition of its metastasis. The aim of this study is notification fertility specialist and stakeholders of malignant disease to inform the role of normal pregnancy, which support immunological response of mothers, special anti-tumor and anti-metastatic mechanism against breast cancer in women. Epidemiological studies in the field of cancer associated with pregnancy history show that pregnancy has a dual impact, short-and long term, on the development of breast cancer; the first, a transient effect the after delivery, stimulates the growth of cancer cells in the early stages of transformation and increases risk of  cancer, a result of a short-term effect of pregnancy. In addition, the increased differen­tiation of stem cells that are capable of forming tumors in the breast due to pregnancy and hormonal changes, reduce the risk of cancer, a phenomenon related to the long-term effect of pregnancy. The immune system of multiparous women due to multiple chimerism that occur as a result of the contact of the maternal immune system with common tumor antigens and embryonic cells, is more powerful  and resistant against breast tumors than their nulliparous counterparts.