Lifestyle factors and risk of breast cancer: A review of randomized trial findings

Abstract

Observational and pre-clinical studies suggest a role for multiple lifestyle factors in the etiology of breast cancer, but few of these have been tested in full-scale randomized trials and fewer still have been shown to affect breast cancer risk. The clearest evidence for a modifiable risk factor is use of menopausal estrogen plus progestin therapy, where randomized trial evidence confirms an increased risk with longer durations of exposure and studies in multiple populations document that a decrease in use results in reduced rates. The effects of estrogen alone on breast cancer risk are less clear as the only large trial on this topic suggests a possible reduction and that timeframe of exposure may be an important effect modifier. The role of diet has not been adequately resolved, in part because of the methodological difficulties. Randomized trial data are strongly suggestive of the benefits of a low-fat diet on breast cancer risk but no other nutrients tested in trials of dietary supplements have yielded benefits for breast cancer or total cancer in women. Similarly, one large randomized trial of low-dose aspirin has not shown an effect on breast cancer. The contrasts between the observational studies that motivated the randomized trials and the results of the trials emphasize the need for more efforts to test other lifestyle factors in full-scale randomized trials. © 2010 Springer-Verlag US.