Menstrual and Reproductive Factors and Risk of Breast Cancer in Iranian Female Population: A Systematic Review and Meta-Analysis

BACKGROUND: Breast cancer (BC) is the most frequent cancer in Iranian females. Due to the changes in lifestyle and reproductive risk factors, the BC incidence rate has been rapidly increasing. Knowing risk factors of BC could significantly contribute to improve preventive behaviors. To investigate the relationship between menstrual and reproductive factors and BC in Iranian female population. METHODS: Web of Science, PubMed, Scopus, and SID as well as references of included studies were searched. Among relevant published observational studies, 27 studies met the inclusion criteria. Pooled risk estimates for the risk factors were determined using random-effects models due to the presence of substantial heterogeneity (P < 0.05). RESULTS: All of the selected studies had case–control design. There was a positive relationship between maternal age at first pregnancy and risk of BC (OR = 1.79 95% CI: 1.36–2.35). Also, menopausal status was associated with higher risk of BC (OR = 1.60 95% CI: 1.18–2.17), whereas, there was no association between menarche age and increased risk of BC (OR = 0.55 95% CI: 0.29–1.03). History of abortion (OR = 1.21 95% CI: 0.97–1.5), nulliparity (OR = 1.43 95% CI: 0.89–2.31), and breastfeeding history (OR = 0.68 95% CI: 0.42–1.09) were not associated with BC risk. CONCLUSIONS: Our findings suggest that age at the first pregnancy and menopausal status were significantly associated with BC risk among Iranian women, whereas menarche age, nulliparity, and history of breastfeeding were not. In regard to the history of abortion, our findings revealed no association with BC, but in high-quality studies, this relationship was significant.