Physical activity and the risk of breast cancer in BRCA1/2 mutation carriers in the Netherlands.

Abstract

Abstract Abstract #505 Background: Physical activity reduces the risk of breast cancer in the general population by 20-40%. Suggested biological mechanisms include a reduction of adipose tissue and decreased lifetime exposure to estrogens. This is one of the first studies that investigates the association between physical activity and breast cancer risk in BRCA1/2 mutation carriers (carriers).
 Patients and methods: We analyzed data from a nationwide retrospective cohort study (GEO-HEBON), including 1026 carriers, of which 465 had a history of breast cancer. We examined the association between breast cancer risk and average (METhr/wk) sports, walking/cycling, occupational, household, and total physical activity, lifetime and for age-periods below and above age 20, separately. All analyses were stratified for birth cohort and gene, clustered on family, and adjusted for confounders and other physical activity variables (when investigating separate components).
 Preliminary results: For adulthood sports activity we found a risk reduction for active carriers (low: Hazard Ratio (HR) = 0.72; 95% CI = 0.54-0.96; medium: HR = 0.64; 95% CI = 0.46-0.90; high: HR = 0.71; 95% CI = 0.48-1.06) when compared to carriers who had never engaged in sports. No risk change was found for sports activity before age 20. For lifetime (mainly adulthood) household activity we found a risk reduction of 0.74 (95% CI = 0.57-0.96) for the second versus the lowest quartile but for higher quartiles HRs were not significantly decreased, and a similar pattern for occupational activity (0.53 (0.35-0.82)). We found neither an effect for walking/cycling activity nor for total physical activity.
 Discussion: Our physical activity information was relatively extensive, and we used proxy-questionnaires to examine survival bias. Limitations include the retrospective character of the cohort and potential misclassification bias. In conclusion, these preliminary results suggest that physical activity may reduce the risk of breast cancer in carriers. The inverse associations were clearest for physical activity during adulthood. Time-dependent, weighted (for testing bias), and stratified (for example by menopausal status and Body Mass Index) analyses will be conducted. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 505.