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HIGHER FITNESS LEVELS and favourable body composition are associated with improved chemotherapy tolerance in breast cancer, according to findings from a large prospective cohort study.
Fitness Levels and Chemotherapy Outcomes
Limited evidence has previously addressed how modifiable lifestyle factors influence chemotherapy delivery and effectiveness. In this study, researchers examined associations between health-related fitness, physical activity, and sedentary behaviour with relative dose intensity and pathologic complete response in patients with newly diagnosed breast cancer receiving neoadjuvant or adjuvant chemotherapy.
The analysis included 890 participants from a prospective cohort, with fitness and body composition measured shortly after diagnosis. Outcomes were derived from medical records, and logistic regression was used to assess associations with relative dose intensity and pathologic complete response.
Body Composition and Relative Dose Intensity
Among participants, 726 individuals, representing 81.6%, achieved a relative dose intensity of 85% or higher. Higher relative dose intensity was negatively associated with markers of adiposity, including body mass index, waist circumference, waist to hip ratio, and fat mass percentage.
Conversely, favourable body composition measures, such as higher lean body mass percentage and lean to fat mass ratio, were positively associated with achieving higher relative dose intensity. In addition, greater cardiorespiratory fitness and muscular strength demonstrated positive dose response relationships with chemotherapy tolerance, indicating that patients with higher aerobic capacity and strength were more likely to receive optimal chemotherapy dosing.
Limited Associations with Treatment Response
With regard to treatment response, fewer consistent associations were identified. A higher lean-to fat mass ratio was positively associated with pathologic complete response. In contrast, body mass index and self-reported physical activity showed negative associations with this outcome.
Overall, the findings suggest that aerobic fitness, muscular strength, and body composition may play an important role in determining chemotherapy tolerability, while their influence on treatment response appears less pronounced. These results highlight the potential relevance of modifiable lifestyle factors in supporting treatment delivery among patients with breast cancer.
Reference
Kokts-Porietis RL et al. Associations of health-related fitness and physical activity with chemotherapy outcomes in breast cancer. British Journal of Cancer. 2026; https://doi.org/10.1038/s41416-026-03384-3.
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