Physical activity and biomarkers in breast cancer survivors: a systematic review.

Breast cancer is the most common cancer among women. The number of breast cancer survivors has increased due to screening and improved treatment methods, which makes it important to increase knowledge on their health and well-being. Physical activity has been reported to improve quality of life, decrease fatigue and reduce all-cause and breast cancer-specific mortality in breast cancer survivors. The beneficial effects of physical activity may manifest themselves in circulating levels of insulin, insulin-growth factors (IGFs) I and II and their binding proteins (IGFBPs), or inflammatory biomarkers. The aim of this report was to review available randomized controlled trials (RCTs) on the effects of physical activity on biomarkers in breast cancer survivors. We identified 12 publications based on nine RCTs that fulfilled our inclusion criteria published until 19th June 2012. The RCTs were small (16-101 breast cancer survivors); mean BMI was ≥25 and the mean age in 8 out of 9 RCTs was approximately 50 years. Five RCTs reported statistically significant effects of physical activity on insulin, IGF-I, IGF-II and IGFBP-3 in breast cancer survivors, but the results were not consistent. None of four RCTs found any evidence for a role of investigated interleukines. One trial reported some evidence that exercise may decrease C-reactive protein levels. In conclusion, available RCTs have produced some evidence that physical activity may result in beneficial changes in levels of insulin, IGFs, IGFBPs, and inflammatory biomarkers in breast cancer survivors. However, further larger RCTs on physical activity and biomarkers in breast cancer survivors are warranted.