Physical activity and survival in breast cancer

Abstract

Purpose: Knowledge about lifestyle factors possibly influencing survival after breast cancer (BC) is paramount. We examined associations between two types of postdiagnosis physical activity (PA) and overall survival after BC.

Patients and methods: We used prospective data on 959 BC survivors from the Diet, Cancer, and Health cohort, all enrolled before diagnosis. Self-reported PA was measured as time per activity, and estimated metabolic equivalent task (MET)-hours per week were summed for each activity. We constructed measures for household, exercise, and total PA. The association between postdiagnosis PA and all-cause mortality was estimated as hazard ratio (HRs) based on Cox proportional hazards model, with time since diagnosis as the underlying time scale. Prediagnosis PA, body mass index (BMI), and receptor status were examined as potential effect modifiers.

Results: We identified 144 deaths from all causes during the study period. In adjusted analyses, exercise PA above eight MET h/week compared to lower levels of activity was significantly associated with improved overall survival (HR, 0.68; confidence interval [CI]: 0.47-0.99). When comparing participation in exercise to non-participation, we found a 44% risk reduction in overall survival (HR, 0.56; CI: 0.33-0.95). Neither between household nor total PA and overall survival did, we find significant associations. Prediagnosis PA, BMI, and receptor status did not modify the effect significantly.

Conclusion: Exercise PA corresponding to 2.5 h or more of brisk weekly walking after BC diagnosis may reduce mortality by up to 32% compared to low-level exercise. Participation in exercise PA may reduce mortality by 44% compared to non-participation.

Keywords: Breast cancer; Physical activity; Survival.