Abstract
It has been suggested that exercise following breast cancer diagnosis is inversely associated with mortality. However, controversy exists regarding the causality of such associations. We evaluated associations of exercise after breast cancer diagnosis with total mortality and recurrence/disease-specific mortality, accounting for conditions that restrict exercise participation. The analysis included 4,826 women with stage I to III breast cancer identified 6 months after diagnosis through the population-based Shanghai Cancer Registry and recruited into the study between 2002 and 2006. Exercise was assessed approximately 6, 18, and 36 months postdiagnosis, and metabolic equivalent (MET) scores were derived. Information on medical history, cancer diagnosis, treatments, quality of life (QOL), anthropometrics, and lifestyles were obtained by in-person interviews at 6 months postdiagnosis. Medical charts were abstracted to verify clinical information. During the median follow-up of 4.3 years, 436 deaths and 450 recurrences/cancer-related deaths were documented. After adjustment for QOL, clinical prognostic factors, and other covariates, exercise during the first 36 months postdiagnosis was inversely associated with total mortality and recurrence/disease-specific mortality with HRs of 0.70 (95% CI: 0.56-0.88) and 0.60 (95% CI: 0.47-0.76), respectively. Significant dose-response relationships between total and recurrence/disease-specific mortality rates and exercise duration and MET scores were observed (all values for P(trend) < 0.05). The exercise-mortality associations were not modified by menopausal status, comorbidity, QOL, or body size assessed at approximately 6 months postdiagnosis. An interaction between disease stage and hormone receptor status and total mortality was noted. Our study suggests that exercise after breast cancer diagnosis may improve overall and disease-free survival.