Population-, intervention- and methodology-related characteristics of clinical trials impact exercise efficacy during adjuvant therapy for breast cancer: a meta-regression analysis.

OBJECTIVE: Significant heterogeneity was highlighted in recent meta-analyses examining exercise effects in cancer patients, suggesting that some characteristics may moderate exercise efficacy. The objectives of this meta-analysis are (1) to investigate the influence of methodology, population and intervention studies' characteristics on the association of exercise with fatigue, quality-of-life (QoL), anxiety and depression; (2) to identify exercise intervention characteristics that may maximize efficacy and evaluate the level of evidence about exercise efficacy in breast cancer patients receiving chemotherapy and/or radiotherapy.
METHODS: Thirty-three randomized controlled trials (RCTs) evaluating exercise were systematically identified. Population, intervention and methodology characteristics were extracted, coded by two independent investigators and tested as moderators of exercise effect in meta-regression models. Psychological outcomes summary effects were then computed by pooling subgroup of RCTs based on categorized moderators.
RESULTS: Indications of selection bias (random sequence generation) or attrition bias (high attrition rate, no intent-to-treat analysis) were associated with better exercise efficacy on QoL, anxiety and depression. Low total prescribed exercise doses (<140 METs.h) or short duration (<16 weeks) interventions yielded fatigue, anxiety and depression reductions whereas higher doses or duration did not. Mind-body interventions led to greater decrease of fatigue and anxiety rather than aerobic/resistance-based interventions.
CONCLUSION: Our findings indicated that exercise-based interventions may improve fatigue, QoL, anxiety and depression, but the evidence mainly rely on studies prone to methodological biases. A prescription of approximately 100 MET.h, e.g. ~120 min of weekly moderate physical exercise for 10 weeks involving mind-body activities, could be advised to maximize fatigue reduction.