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UICC World Cancer Congress 2006

Bridging the Gap: Transforming Knowledge into Action

July 8-12, 2006, Washington, DC, USA

Tuesday, 11 July 2006 - 1:50 PM

Passive and Active Smoking and Breast Cancer: How strong is the evidence?

Kenneth C. Johnson, PhD, Evidence and Risk Assessment Division, Centre for Chronic Disease Prevention and Control, Public Health Agency of Canada, 120 Colonnade Road, Ottawa, ON K1A OK9, Canada and A. Judson Wells, private citizen, 5 Ingleton Circle, Kennett Square, PA 19348, Kennett Square, PA 19348.

Objective: To explore the impact of study design, menopausal status, confounder control and quality of the passive smoking exposure measure on observed risks of breast cancer related to passive and active smoking.

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.

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