Association of pre-diagnosis physical activity with recurrence and mortality among women with breast cancer.

Evidence is emerging that physical activity (PA) may improve overall survival after breast cancer diagnosis. However, the effect of PA on breast cancer recurrence and on cause-specific mortality is less investigated. We assessed the association of pre-diagnosis PA with recurrence, overall and cause-specific survival in a prospective cohort study in Germany including 3,393 non-metastatic breast cancer patients aged 50-74 years. Cox proportional hazards models were calculated adjusted for relevant prognostic factors. During a median follow-up of 5.6 years, 367 patients deceased. Overall mortality was significantly inversely associated with pre-diagnosis recreational PA. However, this effect was mainly attributed to deaths due to causes other than breast cancer. Multiple fractional polynomial analyses yielded a nonlinear association with markedly increased non-breast cancer mortality for women who did not engage in any sports or cycling in the years before the breast cancer diagnosis with a hazard ratio (HR, none vs. any) of 1.71, 95% confidence interval (1.16, 2.52). There were no further risk reductions with increasing activity levels. The association with breast cancer-specific mortality showed a similar dose-response but was far less pronounced with HR (none vs. any) = 1.22 (0.91, 1.64). In contrast, regarding cancer recurrence the dose-response was linear. However, this association was restricted to estrogen/progesterone receptor-negative (ER-/PR-) cases (p interaction = 0.033) with HR (highest vs. no recreational PA) = 0.53 (0.24, 1.16), p trend = 0.0045. Thus, breast cancer patients with a physically inactive lifestyle pre-diagnosis may decease prematurely irrespective of their cancer prognosis. Higher levels of exercise may reduce the risk of recurrence of ER-/PR- breast tumors.