Abstract 135: Coffee consumption increases risk of advanced breast cancer among Singapore Chinese women.
Authors: Zhu Lei , Butler Lesley M. , Wang Renwei , Koh Woon-Puay , Yu Mimi C. , Yuan Jian-Min 
Published: August 2014

Abstract
Background: There is experimental evidence supporting a dual role of coffee-related compounds on breast cancer development. Although reports from prospective epidemiologic studies do not support a relationship between coffee intake and breast cancer risk overall, there is support for an adverse effect among population subgroups defined by body size and stage of disease.
Objective: Using data from a prospective cohort of Chinese women in Singapore, we examined the relationship between coffee intake and breast cancer risk.
Methods: At baseline, between 1993 and 1998, we collected information on dietary history from 35,303 Singaporean Chinese women aged 45 to 74 years. Using Cox regression models, we calculated hazard ratios (HRs) and 95% confidence intervals (CIs) adjusted for potential confounders. Stratified analysis by menopausal status and body mass index (BMI) were conducted to evaluate potential effect modification.
Results: After a mean follow-up of 10 years, 629 women developed breast cancer. Average intake among coffee drinkers (80% of the study population) was 1.5 cups/day (interquartile range = 0.8, 2.3). Women consuming ≥2 cups of coffee per day had a statistically borderline significant increase in risk of breast cancer compared with coffee nondrinkers or monthly drinkers (HR=1.23; 95% CI: 0.98, 1.54; Ptrend=0.11). The positive association strengthened and became statistically significant when the analysis was restricted to advanced breast cancer (n=272) (HR=1.90; 95% CI: 1.30, 2.77; Ptrend&lt;0.01). A similar association was observed for intake of total caffeine; HR was 2.23 (95% CI: 1.52, 3.26) the highest relative to the lowest of caffeine intake (Ptrend&lt;0.01). The associations between coffee and caffeine intake and advanced disease did not differ by menopausal status. In stratified analyses by BMI, the adverse effect of coffee intake on the development of advanced breast cancer was present only among heavier women (BMI &gt; median, 23 kg/m2) (HR=2.35; 95% CI: 1.51, 3.66; P for interaction=0.02). Similar patterns of association were observed with caffeine intake and advanced breast cancer risk by levels of BMI. There was no association with either coffee or caffeine intake and localized breast cancer risk.
Conclusion: We provide the first prospective evidence among an Asian population for the adverse effect of coffee at relatively low levels of intake on the development of advanced breast cancer. Our data suggest that a larger body size may influence the adverse effect of coffee on breast cancer development.
Citation Format: Lei Zhu, Lesley M. Butler, Renwei Wang, Woon-Puay Koh, Mimi C. Yu, Jian-Min Yuan. Coffee consumption increases risk of advanced breast cancer among Singapore Chinese women. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 135. doi:10.1158/1538-7445.AM2013-135