Adult Physical Activity and Breast Cancer Risk in Women with a Family History of Breast Cancer.
Level 3 - non-randomized controlled study
Prospective cohort study
PubMed 30333218 · doi:10.1158/1055-9965.EPI-18-0674
What was done
The Sister Study prospectively followed 50,884 women without personal breast cancer history but with an affected sister. Participants self-reported recreational sport and exercise activity over the prior 12 months. Cox proportional hazards regression was used to calculate hazard ratios (HR) and 95% confidence intervals (CI) for breast cancer risk across hours/week and MET-hours/week of physical activity. Effect modification by extent of family history was assessed using a Bayesian pedigree score.
What was found
Over an average follow-up of 8.4 years, 3,023 breast cancer cases were diagnosed. Higher physical activity was associated with lower postmenopausal breast cancer risk: HR ≥7 vs <1 hours/week was 0.77 (95% CI, 0.66–0.90) and HR for MET-hours/week quartile 4 vs 1 was 0.75 (95% CI, 0.67–0.85). In contrast, physical activity showed a suggestive positive association with premenopausal breast cancer (MET-hours/week quartile 4 vs 1 HR = 1.25; 95% CI, 0.98–1.60), which may have been confined to women with stronger family histories. The protective association for postmenopausal breast cancer did not vary by extent of family history.
Why it matters
This study shows that the protective association between regular physical activity and postmenopausal breast cancer extends to women with an elevated baseline risk due to family history.
Limits
Physical activity was self-reported over the prior 12 months, which introduces potential recall error and misclassification of long-term activity patterns. The premenopausal risk increase had wide confidence intervals crossing 1.0 and requires confirmation. The cohort is restricted to women with an affected sister, which may limit generalizability to other populations.
Cited by
- supports Exercise lowers the risk of developing cancer even in individuals who have a family history of cancer.