Caffeine consumption and the risk of breast cancer in a large prospective cohort of women.

BACKGROUND: Prospective data relating caffeine consumption to breast cancer risk are limited.
METHODS: We evaluated the association between caffeine consumption and breast cancer risk in women enrolled in a completed cancer prevention trial. Detailed dietary information was obtained at baseline (1992-1995) from 38 432 women 45 years or older and free of cancer. During a mean follow-up of 10 years, we identified 1188 invasive breast cancer cases.
RESULTS: Consumption of caffeine and caffeinated beverages and foods was not statistically significantly associated with overall risk of breast cancer. The multivariate relative risks (RRs) of breast cancer were 1.02 (95% confidence interval [CI], 0.84-1.22) for caffeine (top vs bottom quintile), 1.08 (0.89-1.30) for coffee (> or =4 cups daily vs almost never), and 1.03 (0.85-1.25) for tea (> or =2 cups daily vs almost never). However, in women with benign breast disease, a borderline significant positive association with breast cancer risk was observed for the highest quintile of caffeine consumption (RR, 1.32; 95% CI, 0.99-1.76) and for the highest category of coffee consumption (> or =4 cups daily) (1.35; 1.01-1.80); tests for interaction were marginally significant. Caffeine consumption was also significantly positively associated with risk of estrogen receptor-negative and progesterone receptor-negative breast cancer (RR, 1.68; 95% CI, 1.01-2.81) and breast tumors larger than 2 cm (1.79; 1.18-2.72).
CONCLUSIONS: These data show no overall association between caffeine consumption and breast cancer risk. The possibility of increased risk in women with benign breast disease or for tumors that are estrogen and progesterone receptor negative or larger than 2 cm warrants further study.