The Fraction Of Breast Cancer Attributable To Smoking In Norway In 2012. The Norwegian Women And Cancer Study 1991-2012.

Inger GRAM, University of Tromsų (UiT) The Arctic University of Norway, Norway
LITTLE M. 2 , LUND E. 1 , BRAATEN T. 1

1 Department of Community Medicine, Faculty of Health Sciences, Univeristy of Tromsų (UiT) The Arctic University of Norway, Tromsų, Norway
2 Center for Population Sciences, Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, Tennesse, USA

Purpose:  We utilized the Norwegian Women and Cancer Study, a nationally representative prospective cohort study to estimate the fraction of breast cancer attributable to passive and active smoking and the number of breast cancer cases that could have been avoided in the absence of smoking in Norway in 2012.

Methods: We followed 130 503 women, aged 34 to 70 years, who completed a baseline questionnaire between 1991 and 2007, through linkages to national registries through December 2012. We used Cox proportional hazards models to estimate hazard ratios (HRs) with 95% confidence intervals (CIs), while adjusting for confounders. We estimated attributable fractions (AF’s) in smokers and in the population (PAF’s) with 95% CIs.

Results: During a mean follow-up of 13 years, 4 293 women developed invasive breast cancer, confirmed by histology. Compared with never smokers, passive and ever (former and current) smokers had an overall risk of breast cancer that was 18% (HR=1.18, 95% CI 1.05 to 1.33) and 21% (HR=1.21, 95% CI 1.08 to 1.34), respectively. Compared with parous never, excluding passive, smokers, women who had smoked five or more years before giving birth had an overall risk of breast cancer that was 29% (HR=1.29, 95% CI 1.14 to 1.46). The AF for breast cancer was 17.3 (7.4-25.4) for active smokers. The PAF of breast cancer for active smoking was 11.9 (5.3-18.1) overall, and 18.2 (0.9-32.5) for women diagnosed before age 50.

Conclusions: Our study shows that the number of breast cancer cases that may be prevented worldwide is huge. In smokers, one in six and in the population, one in nine breast cancer cases could have been avoided in the absence of smoking. Our findings support the notion that the global cancer burden due to smoking is substantially underestimated.

Funding Sources: None