UICC World Cancer Congress 2006

Methods: 20 published peer-reviewed studies of passive smoking and breast cancer risk were examined. Pooled relative risk estimates for breast cancer were calculated for different subgroups.

Results: The pooled risk estimate for breast cancer associated with passive smoking among life-long nonsmokers was 1.27 (95% confidence interval (CI), 1.11-1.45) (19 studies). The heterogeneity among study results was best explained by the quality of the passive smoking exposure measure. In the subset of 5 studies (all case-control studies) with more complete exposure assessment (quantitative long-term information on the three major sources of passive smoke exposure: childhood, adult residential and occupational), the pooled risk estimate for exposed non-smokers was 1.90 (95% CI, 1.53-2.37).

The overall premenopausal breast cancer risk associated with passive smoking among lifelong nonsmokers was 1.68 (95% CI 1.33-2.12), and 2.19 (95% CI 1.68-2.84) for the 5 of 14 studies with more complete exposure assessment. Statistically increased premenopausal risks were found in 10 (2 cohort, 8 case-control) of 14 studies (71%), in 7 for all exposed women and in 7 for the high-exposure group.

For women who had smoked the breast cancer risk estimate was 1.43 (95% CI 1.12-1.80) when compared to women with neither active nor regular passive smoke exposure; 1.98 (95% CI 1.40-2.81) for more complete passive exposure assessment.