Reproductive factors associated with breast cancer risk in northern Iran.

Breast cancer is a common malignancy for women in most parts of the world and the incidence in Iranian women is growing. The patients are relatively younger than their western counterparts. The aim of study was to investigate the roles of reproductive factors for breast cancer in Babol. In a case-control study in Babol, we recruited a total of 100 new patients with histologically confirmed breast cancer and 200 age-matched controls selected from outpatient clinics. Demographic and reproductive factors were ascertained by in-person interview using a constructed questionnaire. Several potential confounding factors were adjusted using multiple logistic model. The adjusted odds ratio showed that having higher age at first pregnancy and abortion were associated with increased breast cancer risk (the adjusted OR = 4.1, 95% CI: 1.3-13.2 and 2.93, 95% CI: 1.64-5.24, respectively). By increasing parity, the risk had reduced significantly; among women with parity ≥ 5, the adjusted OR was 0.09 (95% CI 0.01-0.7) compared with nulliparous women, and also for each additional parity, the risk reduced by 50% (OR = 0.50, 95% CI: 0.34-0.71). The duration of breast feeding was inversely associated with breast cancer risk, while after additional adjustment for parity, no longer the protective effect of breast feeding was observed. Nulliparity, late age at first birth and abortion were the most important reproductive factors associated with breast cancer risk; therefore, it is recommended to women with these risk factors to perform breast cancer screening tests earlier.