J Li et al. (2011) Coffee Consumption modifies risk of estrogen-receptor negative breast cancer, Breast Cancer Research, published online ahead of print.

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Introduction: Breast cancer is a complex disease and may be sub-divided into
hormone-responsive (estrogen receptor (ER) positive) and non-hormone-responsive
subtypes (ER-negative). Some evidence suggests that heterogeneity exists in the
associations between coffee consumption and breast cancer risk, according to
different estrogen receptor subtypes. We assessed the association between coffee
consumption and postmenopausal breast cancer risk in a large population-based
study (2,818 cases and 3,111 controls), overall, and stratified by ER tumour subtypes.
Methods: Odds ratios (OR) and corresponding 95% confidence intervals (CI) were
estimated using the multivariate logistic regression models fitted to examine breast
cancer risk in a stratified case-control analysis. Heterogeneity among ER subtypes
was evaluated in a case-only analysis, by fitting binary logistic regression models,
treating ER status as a dependent variable, with coffee consumption included as a
covariate.
Results: In the Swedish study, coffee consumption was associated with a modest
decrease in overall breast cancer risk in the age-adjusted model (OR>5 cups/day
compared to OR≤1 cup/day: 0.80, 95% CI: 0.64, 0.99, P trend = 0.028). In the stratified
case-control analyses, a significant reduction in the risk of ER-negative breast cancer
was observed in heavy coffee drinkers (OR>5 cups/day compared to OR≤1 cup/day : 0.43,
95% CI: 0.25, 0.72, P trend = 0.0003) in a multivariate-adjusted model. The breast
cancer risk reduction associated with higher coffee consumption was significantly
higher for ER-negative compared to ER-positive tumours (P heterogeneity (age adjusted)
= 0.004).
Conclusions: A high daily intake of coffee was found to be associated with a
statistically significant decrease in ER-negative breast cancer among
postmenopausal women.

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