A new study has reported that high levels of physical activity may improve survival in postmenopausal women with breast cancer, even among those reporting low levels of physical activity prior to diagnosis. The study was designed to examine how prediagnosis and postdiagnosis physical activity and changes in prediagnosis to postdiagnosis physical activity relate to survival in postmenopausal women. Although previous studies have reported that physically active breast cancer survivors have lower rates of death from all causes, the association between change in physical activity from before to after diagnosis and mortality has not been established. The study included 4,643 women diagnosed with invasive breast cancer after having enrolled in the Women's Health Initiative study of postmenopausal women. Physical activity from recreation and walking was measured at baseline (prediagnosis) and after diagnosis of breast cancer (assessed at the three-year or six-year post-baseline visit).

Women participating in nine or more MET (metabolic equivalent) hours per week of physical activity (which amounts to approximately three hours per week of fast walking) before diagnosis of breast cancer were found to have a 39% lower risk of death from all causes compared to inactive women. Study participants engaging in this level of physical activity after diagnosis also had a 39% lower risk of breast cancer-specific death and 56% lower risk of death from any causes than inactive women. It was also found that women who increased or maintained physical activity of at least nine MET hours per week after diagnosis had a 33% lower risk of death from all causes than inactive women. This was true even of women who had been inactive before diagnosis. The authors conclude that women diagnosed with breast cancer should be encouraged to initiate and maintain a program of physical activity.