Objective To give an up-to-date assessment of the association
of alcohol with female breast cancer, addressing
methodological issues and shortfalls in previous overviews.
Methods Meta-analysis of studies (any language) providing
original data on incidence of first primary breast
cancer and alcohol. Two reviewers independently extracted
data. Study quality assessed by objective criteria including
degree of control for confounding; funnel plots examined
for publication bias; meta-regression techniques to explore
heterogeneity. Risks associated with drinking versus not
drinking and dose–response not constrained through the
origin estimated using random effects methods.
Results Ninety-eight unique studies were included,
involving 75,728 and 60,653 cases in drinker versus nondrinker
and dose–response analyses, respectively. Findings
were robust to study design and analytic approaches in the
meta-analyses. For studies judged high quality, controlled
for appropriate confounders, excess risk associated with
alcohol drinking was 22% (95% CI: 9–37%); each additional
10 g ethanol/day was associated with risk higher by
10% (95% CI: 5–15%). There was no evidence of publication
bias. Risk did not differ significantly by beverage
type or menopausal status. Estimated population attributable
risks were 1.6 and 6.0% in USA and UK, respectively.
Conclusions Taking account of shortcomings in the study
base and methodological concerns, we confirm the alcohol–breast
cancer association. We compared our results to
those of an individual patient data analysis, with similar
findings. We conclude that the association between alcohol
and breast cancer may be causal.