Physical activity before and after breast cancer diagnosis and survival - the Norwegian women and cancer cohort study
Methods: We included 1,327 women with breast cancer from the population-based Norwegian Women and Cancer study, which enrolled women from 1991 to 2003. Breast cancer cases were identified through linkage to the Cancer Registry of Norway; date and cause of death were obtained from the National Register for Causes of Death through 31 December 2012. Self-reported pre- and post-diagnostic PA levels were assessed, and Cox proportional hazard regression and spline regression were used to evaluate the associations.
Results: Pre-diagnostic PA levels were not associated with all-cause or breast cancer-specific mortality. Post-diagnostic PA levels were associated with a significant trend (P < 0.001) of decreased all-cause and breast cancer-specific mortality, which was stronger among older women (aged 50–74 years) and did not differ across categories of body mass index. All-cause mortality (hazard ratio [HR] = 1.76, 95 % confidence interval [CI] 1.21–2.56) and breast cancer-specific mortality (HR = 2.05, 95 % CI 1.35–3.10) increased among women who reduced their post-diagnostic PA level. These values were similar among women whose maintained an inactive PA level pre- and post-diagnosis.
Conclusion: Overall, we observed a dose–response trend, with an inverse association between increased postdiagnostic PA level and all-cause and breast cancer-specific mortality, as well as a higher mortality risk among women who reduced their post-diagnostic PA levels. Our results are very promising for women with breast cancer, and indicate that health care professionals should consider adding PA as a part of primary cancer treatment.