As reported in the Journal of Clinical Oncology by Timmins et al, a pooled analysis of 19 international cohorts showed that high vs low self-reported leisure-time physical activity was associated with a reduced risk of premenopausal breast cancer.
Study Details
The study used individual-level data from 19 cohort studies comprising 547,601 premenopausal women; among these, 10,231 developed incident breast cancer. Hazard ratios for high vs low levels of activity were based on comparison of risk at the 90th (high) vs 10th (low) percentiles of activity.
Key Findings
Median follow-up was 11.5 years (interquartile range = 8.0–16.1 years). Patients with high levels of activity had a significant 6% reduction in breast cancer risk vs those with low levels of activity (hazard ratio [HR] = 0.94, 95% confidence interval [CI] = 0.89–0.99) before adjustment for body mass index (BMI) and a significant 10% risk reduction (HR = 0.90, 95% CI = 0.85–0.95) after adjustment for BMI. Tests of nonlinearity suggested an approximately linear relationship between activity and risk (P = .94 for nonlinearity).
The effect of exercise in reducing cancer risk was particularly notable in risk for HER2-enriched breast cancer (HR = 0.57, 95% CI = 0.39–0.84, P = .07 for heterogeneity). Associations between activity level and breast cancer risk did not vary significantly across strata of breast cancer risk factors, including subgroups of adiposity.
The investigators concluded, “This large, pooled analysis of cohort studies adds to evidence that engagement in higher levels of leisure-time physical activity may lead to reduced premenopausal breast cancer risk.”
Anthony J. Swerdlow, PhD, of the Division of Genetics and Epidemiology, The Institute of Cancer Research, London, is the corresponding author for the Journal of Clinical Oncology article.
Disclosure: The study was supported by Breast Cancer Now, United Kingdom National Health Service funding, U.S. National Cancer Institute, and others. For full disclosures of the study authors, visit ascopubs.org.
