Reproductive Risk Factors of Breast Cancer among Women in Tehran and Northwest of Iran: A Case-Control Study

Background and Objectives: Reproductive factors are in close relationship with breast carcinogenesis. This matched case-control study was conducted to study the association of reproductive risk factors with the risk of breast cancer (BC) among women in Tehran and northwest of Iran. Methods: This hospital-based case-control study was performed on a total of 432 patients diagnosed with BC with confirmed histopathology who were recruited from hospitals affiliated with Shahid Beheshti and Tabriz University of Medical Sciences between 2007 and 2012, and 543 regionally matched controls without a prior history of BC. Results: The average number of pregnancy and breast-fed children were significantly higher in cases than controls (P<0.01). The duration of breast-feeding was longer in patients (18.0±8.4 months) than controls (16.0±9.1; P<0.001). Most of the patients were diagnosed with BC above the age of 48 years old which was higher than the mean age of the recruited matched controls. Older age was associated with a 3.87 higher risks of BC development (95% CI: 2.94-5.10). The higher frequency of lactation in patients was significantly associated with the elevated risk (OR=2.22, 95% CI 1.62-3.04). The duration of breast-feeding within14-24 months was correlated with OR=0.52 to protect BC development during the reproductive age (<48 years) (95% CI: 0.32-0.86). Conclusion: High frequency of pregnancy, lactation, and older ages at first pregnancy are associated with the risk of BC, while older age at puberty, menopause, and longer duration of breast-feeding (age above 48 years) have inverse associations with the risk of BC.