Background: Using a secondary data analysis from randomized controlled trials comparing one year of resistance exercise (n ¼ 109) to a placebo control condition (n ¼ 106) in postmenopausal, posttreatment breast cancer survivors, we investigated the influence of resistance training and changes in body composition on markers associated with cancer progression. Methods: Measures included serum levels of insulin, IGF-1, IGFBP1-3, leptin, serum amyloid A (SAA), adiponectin, C-reactive protein (CRP), IL1b, TNFa, IL6, and IL8, and body composition (total, lean and fat mass in kg) by DXA at baseline, 6, and 12 months. Linear mixed effects models were used to examine the association between group, biomarkers, and body composition and whether or not changes in muscle strength or body composition influenced the effect of exercise on biomarkers. Results: CRP decreased over time among women participating in resistance training compared with increases in controls (P ¼ 0.045). In stratified analyses and compared with increases in controls, women who gained strength reduced CRP (P ¼ 0.003) and maintained levels of IL1b and IL6. Among exercisers who lost weight (2 kg), CRP (P ¼ 0.045), leptin (P < 0.01), and SAA (P ¼ 0.029) decreased, whereas IGF- BP1 (P ¼ 0.036) increased compared with controls. Conclusions: Resistance training May lower inflammation and improve insulin pathway profiles, but the magnitude and degree of benefit from exercise May depend upon whether or not women gained strength, a possible marker of compliance with training, and/or lost weight during exercise. Impact: Future resistance training trials should consider these potential influencing factors as they May determine how well exercise can slow cancer progression and prevent disease recurrence. Cancer Epidemiol Biomarkers Prev; 27(2); 146–53. 2017 AACR.
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