Exercise training in breast cancer survivors: a review of trials examining anthropometric and obesity-related biomarkers of breast cancer risk

Background: Substantial observational evidence exists which supports a role for physical activity in improving breast cancer prognosis. Biological pathways linking physical activity to prognosis include alterations in obesity-related biomarkers involving chronic low-grade inflammation, adipokines, and markers of insulin resistance. Exercise interventions, with these biomarkers as end-points, may be beneficial for improving breast cancer outcomes. Objective: To conduct a systematic literature review, investigating the effect of exercise interventions on anthropometric variables and related biomarkers of cancer risk in breast cancer survivors. Methods: The preferred reporting for systematic review and meta-analysis (PRISMA) guidelines were followed. A comprehensive literatures search was conducted using the databases PubMed, Embase, SciVerse, the Cochrane Library, AMED, and PEDro, for articles published in English up to June 2012. Exercise interventions, both randomized and non-randomized, examining a range of biomarkers of cancer risk were included. Results: Thirteen articles, representing nine exercise interventions were included - seven randomized controlled trials (RCT) and two non-randomized trials. A number of trials reported improvements in anthropometrics (percentage body fat, body mass index, and waist / hip circumference). Three trials reported changes in insulin-like growth factor (IGF)-I and IGF-II, and insulin-like growth factor binding protein (IGFBP)-3. There were no reported changes in insulin, glucose, insulin resistance, adipokines or inflammatory markers. Conclusions: More robust RCTs are required to fully elucidate the effect of exercise training on biomarkers of breast cancer risk and determine the role of physical activity as an adjunct to breast cancer treatment as a means of reducing breast cancer recurrence and improving mortality.