Does Physical Activity Differentially Influence Physical Function In Younger Versus Older Women With Breast Cancer?

Abstract

Higher levels of self-reported physical activity (PA) are associated with lower risk of breast cancer. To date, however, only one prospective study has examined the association between accelerometer-measured PA, an objective and more precise measure of PA, and incident breast cancer. PURPOSE: To examine the associations between accelerometer-measured total, light, and moderate-to-vigorous PA (MVPA) and incident breast cancer among postmenopausal women in the United States (US) Women's Health Accelerometry Collaboration (WHAC). METHODS: The WHAC comprised 21,091 women including 15,376 from the Women's Health Study [WHS; mean age 71.4±5.7 years; 95.2% non-Hispanic White] and 5,715 from the Women's Health Initiative Objective Physical Activity and Cardiovascular Health Study [OPACH; mean age 78.7±6.7 years; 50.0% non-Hispanic White]. All women wore an ActiGraph GT3X+ on the hip for ≥10 hours on ≥4 of 7 days during 2011-2015 and were followed for 5.9 average years to identify physician-adjudicated in situ (n=79) or invasive (n=491) breast cancers. Calibrated intensity cut points were used to define minutes per day of light and MVPA, which were summed to calculate total PA. Multivariable Cox regression estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for tertiles of wear time-standardized PA in association with incident in situ and invasive breast cancer, overall, by age (<75 or ≥75 years), and by cohort (WHS or OPACH). RESULTS: Overall, the highest (vs. lowest) tertiles of total, light, and MVPA were associated with breast cancer HRs (95% CIs) of 0.85 (0.68-1.04), 0.92 (0.75-1.13), and 0.81 (0.64-1.03), respectively. By age, HRs for MVPA were more pronounced among women <75 years (HR=0.73, 0.55-0.97) than among women ≥75 years (HR=1.18, 0.76-1.84; P Interaction =0.04). Associations did not differ significantly by cohort. CONCLUSION: Overall, no strong association was observed between accelerometer-measured PA and breast cancer. Among women ages <75 years, engaging in higher levels of MVPA, but not light PA, had an inverse association with breast cancer. Additional studies of accelerometer-measured PA and breast cancer by cancer characteristics such as stage at diagnosis and receptor status are needed.