Abstract
Energy balance is associated with risk of development of many common cancers, and with clinical outcomes after cancer diagnosis in several solid tumors. Higher BMI leads to an increased risk of most solid tumors and hematologic malignancies. Exceptions in both sexes include lung and esophageal cancer; in women they also include premenopausal breast cancer (Renehan et al Lancet 2008). Physical inactivity has been convincingly or probably associated with increased risk of cancer of the breast, colon and endometrial cancer and possibly associated with an increased risk of lung, prostate and ovarian cancers; it has been estimated risk of these cancers might be reduced by 20–30% in active individuals (Friedenreich C et al Eur J Cancer 2010). Furthermore, observational data suggest that cancer risk may be reduced in obese individuals who undergo bariatric surgery (Renehan Lancet Oncology 2009) and that risk of obesity-related cancers (breast, colon, endometrial, any obesity associated cancer) is reduced in individuals reported an intentional weight loss of 20 pounds or more. Similar associations have been reported in patients diagnosed with several common types of cancer. For example, higher BMI has been convincingly associated with poor breast cancer outcomes; meta-analyses suggest relative risk of recurrence or death is increased by 25–40% in obese women. Evidence is less convincing for colorectal cancer; obesity may be associated with prostate cancer having more aggressive characteristics. Higher levels of physical activity pre and/or post diagnosis have been associated with improved outcomes in breast and colorectal cancer. One randomized trial involving 2437 early stage breast cancer patients reported improved relapse free survival (HR 0.96, 95%CI 0.60–0.98) in those randomized to a reduced fat diet (associated with modest weight loss) versus controls. A second RCT in breast cancer survivors failed to identify a prognostic effect of a more complex dietary intervention that lowered fat intake but was not associated with weight loss. Intervention studies have convincingly demonstrated that modification of energy balance (physical activity, dietary change, weight loss) in cancer patients is feasible, particularly in those with breast cancer, but confirmation of beneficial effects on cancer outcomes is lacking. Potential physiologic mediators of prognostic effects of energy balance include members of the insulin/insulin-like growth factor pathway, inflammation, adipocytokines and sex hormones; it is likely the relative importance of these factors varies across tumor types. Large scale intervention studies targeting energy balance, its components (e.g. physical activity) and/or key physiologic mediators are needed to provide high level evidence regarding benefits of modifying energy balance, or its physiologic mediators. One study targeting insulin (MA32) is underway in breast cancer survivors; others have been proposed.
Citation Information: Cancer Prev Res 2011;4(10 Suppl):PL02-02.
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