Weight, physical activity and breast cancer survival.

Weight, weight change and physical activity may affect prognosis among women who are diagnosed with breast cancer. Observational studies show associations between overweight/obesity and weight gain with several measures of reduced prognosis in women with breast cancer, and some suggestions of lower survival in women who are underweight or who experience unexplained weight loss after diagnosis. Observational studies have also shown an association between higher levels of physical activity and reduced breast cancer-specific and all-cause mortality, although a dose-response relationship has not been established. The effects of purposive dietary weight loss and increase in physical activity on survival or recurrence in breast cancer are not yet established, and randomised controlled trials are needed for definitive data. This paper presents the epidemiologic evidence on weight status, weight change, and physical activity and breast cancer survival; suggests potential mediating mechanisms; summarises evidence on weight loss interventions in breast cancer survivors; describes ongoing randomised clinical trials designed to test the effects of weight loss or physical activity on breast cancer survival; and provides information on available guidelines on weight and physical activity for cancer survivors.