Hormonal and Body-Size Factors in Relation to Breast Cancer Risk: A Prospective Study of 11,889 Women in a Low-Incidence Area

Purpose This prospective cohort study of 11,889 women was conducted to determine significant factors associated with the risk of breast cancer among Chinese women in Taiwan, a low-incidence area. Methods In-person interviews were completed for subjects to solicit information on hormonal factors. Measurements of height, weight, and waist-and- hip circumferences were performed by well-trained assistants using standardized techniques. Cox proportional hazards models were employed to estimate relative risks (RRs) and 95% confidence intervals (CIs). Results During an average follow-up time of 10.3 years (range: 1 to 11 years) with an accumulation of 134,063 person-years, 104 incident breast cancer cases were identified through data linkage with national cancer registry profile. There was a significant elevation in breast-cancer risk with increasing duration of the interval between age at menarche and age at first full-term pregnancy (FFTP). Additionally, central adiposity reflected by hip circumference was a significant predictor of breast cancer in this Chinese female population. Conclusions The findings of this study indicated common mechanisms responsible for the higher incidence of breast cancer in Western populations may also explain the risk of breast cancer development in Taiwan, a low-incidence area.