The Relationship between Reproductive Factors and Breast Cancer in Women Aged 35 to 70 Years: Results of the First Phase of Shahedyeh Cohort Study in Yazd Province

The identification of risk factors for breast cancer has an important role in examining the status of cancer care system. Therefore, the present study was conducted to determine the relationship between reproductive factors and breast cancer in women aged 35 to 70 years based on the data from the first phase of Shahedyeh Cohort Study (SCS) in Yazd province.

This descriptive, cross-sectional study was conducted using the data from the first phase of SCS in Yazd province in 2015-2017. In this study, 4820 women aged 35 to 70 years were investigated, including 25 (0.6%) with a history of breast cancer and 4795 (99.4%) without any history of breast cancer. The data used in this study included demographic and reproductive histories of the women. The data were analyzed using Chi-square, t-test, and logistic regression.

The results showed that breastfeeding for less than 11 months increases the chance of breast cancer by 2.78 times, hormone therapy after menopause by 2.07 times, the onset age of menopause ≥46 by 1.71 times, having a history of abortion by 1.63 times, taking contraceptive pills by 1.59 times, age at menarche ≤13 by 1.49 times, and being overweight and obesity by 1.45 times.

According to the results, breastfeeding for less than 11 months, hormone therapy after menopause, the onset age of menopause after 46 years, and taking contraceptive pills were the most important risk factors for breast cancer.