Relationship between pregnancy-associated variables and breast cancer risk: A systematic review

Globally, breast cancer is the most common malignancy causing extensive mortality in women. In most cases, there is no known risk factor for breast cancer. Extensive hormonal changes that occur during pregnancy appear to be involved in the etiology of breast cancer. Since identifying risk factors helps with primary prevention and early diagnosis of breast cancer, this study was performed to systematically review studies about pregnancy-related variables and the risk of breast cancer in Iran and worldwide.
In this systematic review, we searched PubMed, Google Scholar, Scopus, SID, and Science Direct databases using keywords of “pregnancy-related variables” and “breast cancer” to retrieve articles published during 2000-2017. Then, those articles that obtained a score of ≥ 6 based on the Newcastle–Ottawa Scale were entered to the study. The results were reported qualitatively.
Fifty articles consisting of 26 case-controls and 24 cohort articles, which met the inclusion criteria, were investigated. Our evaluations indicated that among the factors examined, abortion and preeclampsia had a stronger relationship with breast cancer.
History of abortion seems to increase the risk of breast cancer. Also, history of preeclampsia plays a protective role in breast cancer. Further studies are needed to examine the relationship of gestational diabetes and multiple gestations with breast cancer.