Introduction: Breast cancer is known to be the second cause of death in the world and the third cause of death among Iranian women. Pregnancy has been regarded as one of the influential factors that contributes to
breast cancer due to the strong hormonal changes it causes in the body. The present review article aims at investigating the effect of
pregnancy hormones on decreasing the risk of breast cancer.Methods: The present review article used the keywords pregnancy, breast cancer, prolactin, and strogen in the following international databases: Sid, PubMed, Scopus, Mag Iran, Google Scholar, Web of Science, Science Direct to search for articles. Sixty articles were extracted and after examining the entry and exit criteria based on Prisma Checklist, 10 of the articles were removed and finally, 50 of the selected articles from 2000 to 2017 reached the criteria and data were extracted from them.Results: The amounts of Growth Hormones, Estradiol, and
Prolactin all change during pregnancy. Moreover, by changing the stem cells and strengthening the body against tumor,
pregnancy can decrease the chance of transformation of breast’s epithelium progenitors. However, the studies in the literature suggest that most of the cancerous tumors have both
Estrogen receptor and prolactin or just either of them, and since in the first stage both
Estrogen and
Prolactin get attached to the membrane receptors and will lead to gene expression through the nucleus and as a result make changes in tissues that have tumors, the existence of
Estrogen and
Prolactin will cause the cancerous tumor to become malignant. Hence, due to the proliferation of these two hormones during pregnancy, the
pregnancy itself cannot be regarded as a contributing factor to the decrease of cancer risk.Conclusions: Pregnancy can be regarded as a contributing factor to the decrease of cancer risk only when there is no trace of a cancerous tumor prior to pregnancy. In case a tumor exists prior to pregnancy, then
pregnancy can be considered as an influential factor in causing the tumor to become a malignant one.