Population attributable risk of modifiable risk factors associated with invasive breast cancer in women aged 45-69 years in Queensland, Australia

Objectives To quantify the population attributable risk of key modifiable risk factors associated with breast cancer incidence in Queensland, Australia. Study design Population attributable fractions (PAFs) for high body mass index (BMI), use of hormone replacement therapy (HRT), alcohol consumption and inadequate physical activity were calculated, using prevalence data from a representative survey of women attending mammographic screening at BreastScreen Queensland in 2008 and relative risk estimates sourced from published literature. Attributable cancers were calculated using 'underlying' breast cancer incidence data for 2008 based on Poisson regression models, adjusting for the inflation of incidence due to the effects of mammographic screening. Main outcome measures Attributable burden of breast cancer due to high body mass index (BMI), use of hormone replacement therapy (HRT), alcohol consumption and inadequate physical activity. Results In Queensland women aged 45-69 years, an estimated 12.1% (95% CI: 11.6-12.5%) of invasive breast cancers were attributable to high BMI in post-menopausal women who have never used HRT; 2.8% (95% CI: 2.7-2.9%) to alcohol consumption; 7.6% (95% CI: 7.4-7.9%) to inadequate physical activity in post-menopausal women and 6.2% (95% CI: 5.5-7.0%) to current use of HRT after stratification by BMI and type of HRT used. Combined, just over one quarter (26.0%; 95% CI: 25.4-26.6%) of all invasive breast cancers in Queensland women aged 45-69 years in 2008 were attributable to these modifiable risk factors. Conclusions There is benefit in targeting prevention strategies to modify lifestyle behaviours around BMI, physical activity, HRT use and alcohol consumption, as a reduction in these risk factors could decrease invasive breast cancer incidence in the Queensland population.