Abstract
BACKGROUND: The effects of exercise on cancer outcomes may differ depending on its positioning within different cancer treatment combinations. We examined whether the associations between physical activity (PA) and cancer outcomes varied by cancer treatment modality or timing of PA. METHODS: We conducted a secondary analysis of the Prostate Cancer Cohort Study consisting of 830 men in Alberta, Canada with newly diagnosed prostate cancer. Lifetime prediagnosis PA was assessed by an in-person interview shortly after diagnosis whereas postdiagnosis PA was assessed at 2-3 year intervals by an in-person interview (first follow-up) or self-report (second and third follow-ups). Cox proportional hazards regression models were used to test interactions between PA and treatment modalities for disease-free survival, overall survival, and prostate cancer-specific disease-free survival. RESULTS: Postdiagnosis vigorous PA significantly interacted with surgery (p < 0.001) and radiotherapy (p = 0.003). Specifically, patients who had surgery experienced a 61% lower likelihood of a disease-free survival event if they engaged in any versus no postdiagnosis vigorous PA (HR = 0.39, 95% CI = 0.27-0.57). Conversely, patients who received radiotherapy did not experience any benefit from postdiagnosis vigorous PA (HR = 1.14, 95% CI = 0.88-1.47). CONCLUSIONS: The role of PA as a treatment for prostate cancer may depend on its combination and sequencing with other treatments.