Associations of health-related fitness and physical activity with chemotherapy outcomes in breast cancer

Background: Limited research exists on how modifiable lifestyle factors influence tolerability and response to chemotherapy. We investigated the associations between health-related fitness, physical activity, and sedentary behaviour after diagnosis with relative dose intensity (RDI) and pathologic complete response (pCR) among newly diagnosed breast cancer patients who received neoadjuvant or adjuvant chemotherapy. Methods: This analysis includes 890 participants of the Alberta Moving Beyond Breast Cancer prospective cohort study who received chemotherapy. We directly measured cardiorespiratory fitness, muscular strength and endurance, body composition, physical activity, sedentary behaviour shortly after diagnosis and abstracted RDI and pCR data from medical charts. We used logistic regression to measure the associations with RDI (< 85%, ≥ 85%) and pCR (no, yes). Results: Of 890 participants, 726 (81.6%) achieved ≥85% RDI. We found negative linear associations between ≥ 85% RDI and greater body mass index (BMI), waist circumference, waist-to-hip ratio and fat mass percentage; and positive linear associations for greater lean body mass percentage and lean-to-fat mass ratio. We observed positive dose-response relationships between ≥ 85% RDI and relative VO_2peak, upper body and lower body strength. Higher lean-to-fat mass ratio was positively associated with pCR, in contrast to negative associations for BMI and self-reported physical activity. Conclusion: Greater relative aerobic fitness, muscular strength, and healthy body composition were consistently associated with better chemotherapy tolerance whereas fewer associations were found with chemotherapy response.