Comparison of women's breast cancer risk factors in Geneva, Switzerland and Shanghai, China

BackgroundWe compared the prevalence of known and suspected breast cancer risk factors among women in Geneva, Switzerland, where the annual incidence of breast cancer is high, to women in Shanghai, China, where incidence is lower.MethodsDifferent translations of the same woman's health questionnaire were administered to women aged 35 to 74 years in Shanghai (n = 631) and Geneva (n = 1,212) during 1996–1997 and reproductive and lifestyle factors compared.ResultsShanghai women reported older age at menarche (median 15 vs. 13 years), fewer nulliparity (7.3 vs. 21.6%), younger age at first live birth (median 25.7 vs. 28.4 years), and shorter duration of reproductive life (median 35.7 vs. 38.4 years). Geneva women had a greater prevalence of current cigarette smoking (22.4 vs. 1.8%), oral contraceptive use (61.1 vs. 10.0%), hormone replacement therapy use (23.4 vs. 0.8%), and family history of breast cancer (8.6 vs. 1.4%). Among women who breastfed, Shanghai women had more than twice the duration of breastfeeding than Geneva women (median 48 vs. 21 weeks).ConclusionsDifferences in the prevalence of breast cancer risk factors, in particular reproductive characteristics, may contribute to the large contrast in cumulative risk between women living in Geneva and Shanghai.