Ethnic and biological differences in the association between physical activity and survival after breast cancer

Abstract

Physical activity is recommended for most cancer patients as a nonpharmacological therapy to improve prognosis. Few studies have investigated the association between physical activity and breast cancer prognosis by ethnicity, biological, and modifiable risk factors for mortality. We investigated the association between physical activity and long-term survival among breast cancer survivors. A total of 397 survivors (96 Hispanic and 301 non-Hispanic White (NHW)) from the New Mexico HEAL study contributed baseline and biological data approximately 6 months after diagnosis. Study outcomes included all-cause, breast cancer-specific, and non-breast cancer mortality. The exposure was self-reported physical activity within the past month. Multivariable hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox Proportional Hazards regression. A total of 133 deaths (53 breast cancer-specific deaths) were observed after a median follow-up time of 13 years. Engaging in >6.9 metabolic equivalent hours/week (MET-h/week) of moderate to vigorous physical activity (active) was inversely associated with all-cause mortality among all women (HR 0.66, 95% CI 0.43-0.99) and NHWs (HR 0.58, 95% CI 0.36-0.94). Active NHW women also had a reduced risk of non-breast cancer mortality (HR 0.56, 95% CI 0.31-0.99), compared to inactive women (0 MET-h/week). In subgroups, we observed the inverse associations with all-cause mortality among women >58 years old (p-interaction= 0.03) and with localized stage (p-interaction = 0.046). Our results confirm the protective association between physical activity and mortality after breast cancer diagnosis, and demonstrate that this association significantly differs by age and cancer stage. Larger studies are warranted to substantiate our findings.

Keywords: Cancer epidemiology; Risk factors.

Fig. 1. Associations between all-cause mortality and physical activity during the past month stratified by biological and clinical factors.

The blue square and lines denotes HRs and 95% CIs for 0-6.9 MET hours/week compared to the reference group of 0 MET hours/week. The red circle andlines denotes HRs for greater than 6.9 MET hours/week compared to the reference group. The p values for statistical interactions are included for each variable. ¶ Models adjusted for age, disease stage at baseline, treatment, BMI, diabetes, fructosamine and ethnicity, * p < 0.05, # p for the interaction term < 0.05, indicating the statistically significant difference of the impact of moderate to vigorous physical activity on survival across subgroups.