Coffee and black tea consumption and risk of breast cancer by estrogen and progesterone receptor status in a Swedish cohort.

BACKGROUND: Coffee and tea consumption has been inconsistently associated with the risk of breast cancer. We examined the associations of caffeinated coffee and black tea consumption with the incidence of breast cancer, overall and by estrogen receptor (ER) and progesterone receptor (PR) status of the tumor, in the Swedish Mammography Cohort. METHODS: We prospectively followed up 61,433 women who were cancer free at baseline in 1987-1990. Coffee and tea consumption was assessed with a food-frequency questionnaire administered at baseline and in 1997. Incident invasive breast cancer cases were ascertained by linkage with Swedish Cancer registers. RESULTS: Over a mean follow-up of 17.4 years, through December 2007, there were 2,952 incident cases of invasive breast cancer identified. Coffee consumption was not associated with risk of overall breast cancer (multivariate relative risk (RR) for ≥ 4 cups/day versus <1 cup/day = 1.02; 95% CI, 0.87-1.20) or with any subtype defined by ER and PR status. Black tea consumption was significantly positively associated with risk of overall breast cancer and ER+/PR+ tumors. The multivariate RRs comparing ≥ 2 cups/day of tea with no consumption were 1.22 (95% CI, 1.05-1.42) for overall breast cancer and 1.36 (95% CI, 1.09-1.69) for ER+/PR+ tumors. CONCLUSION: Findings from this prospective study do not support a role of coffee consumption in the development of breast cancer but suggest that black tea consumption may be positively associated with risk of ER+/PR+ tumors.