Lani
12-29-2006, 01:41 PM
December 29, 2006 — Postmenopausal women may lower their risk of developing breast cancer by engaging in moderate exercise, according to the results of a prospective cohort study reported in the December issue of the Archives of Internal Medicine.
"Physical activity is a potentially modifiable breast cancer risk factor," write Aditya Bardia, MD, MPH, from the Mayo Clinic College of Medicine in Rochester, Minnesota, and colleagues. "There is considerable recent evidence to suggest that risk factors for breast cancer differ based on its subtype, particularly estrogen receptor(ER)/progesterone receptor (PR) status, but this has been less well studied for physical activity. The objective of this study was to examine the association of physical activity with breast cancer incidence based on ER/PR status of the tumor."
In the Iowa Women's Health Study, 41,836 postmenopausal women self-reported recreational physical activity on the baseline questionnaire, and they were classified into 3 levels (high, medium, and low). Through linkage with the Iowa Surveillance, Epidemiology, and End Results Cancer Registry, the investigators determined breast cancer incidence and ER/PR status during 18 years of follow-up. Cox proportional hazards models were used to estimate multivariate relative risks (RRs) of breast cancer, after adjustment for other breast cancer risk factors.
During 554,819 person-years of follow-up, there were 2548 incident cases of breast cancer. Compared with low levels of physical activity, high physical activity levels were inversely associated with risk for breast cancer (RR, 0.86; 95% confidence interval [CI], 0.78 - 0.96). There were inverse associations for ER+/PR+ (RR, 0.87; 95% CI, 0.75 - 1.00), ER+/PR- (RR, 0.67; 95% CI, 0.47 - 0.96), and ER-/PR- (RR, 0.80; 95% CI, 0.56 - 1.14) tumors.
Although further adjustment for body mass index decreased the overall association with breast cancer (RR, 0.91; 95% CI, 0.82 - 1.01) and for ER+/PR+ tumors (RR, 0.94; 95% CI, 0.81 - 1.08), there was no change for ER+/PR- tumors (RR, 0.66; 95% CI, 0.46 - 0.94).
Study limitations include physical activity measured as a single self-reported assessment at baseline, with no update during follow-up, lack of data on detailed aspects of physical activity, inability to calculate metabolic equivalents, information about ER/PR status obtained through multiple pathological laboratories rather than a single reference laboratory, and a predominantly white study population.
"Higher recreational physical activity might reduce the risk of postmenopausal breast cancer overall," the authors write. "Risk reduction varies by ER/PR status of the tumor, being most marked for ER+/PR- tumors, which, in general, have been associated with a clinically more aggressive tumor phenotype. If confirmed in additional studies, these results would suggest that additional mechanisms, besides an effect on body mass, may account for observed protective effects of physical activity in reducing breast cancer."
The National Cancer Institute supported this study in part. The authors have disclosed no relevant financial relationships.
Arch Intern Med. 2006;166:2478-2483.
"Physical activity is a potentially modifiable breast cancer risk factor," write Aditya Bardia, MD, MPH, from the Mayo Clinic College of Medicine in Rochester, Minnesota, and colleagues. "There is considerable recent evidence to suggest that risk factors for breast cancer differ based on its subtype, particularly estrogen receptor(ER)/progesterone receptor (PR) status, but this has been less well studied for physical activity. The objective of this study was to examine the association of physical activity with breast cancer incidence based on ER/PR status of the tumor."
In the Iowa Women's Health Study, 41,836 postmenopausal women self-reported recreational physical activity on the baseline questionnaire, and they were classified into 3 levels (high, medium, and low). Through linkage with the Iowa Surveillance, Epidemiology, and End Results Cancer Registry, the investigators determined breast cancer incidence and ER/PR status during 18 years of follow-up. Cox proportional hazards models were used to estimate multivariate relative risks (RRs) of breast cancer, after adjustment for other breast cancer risk factors.
During 554,819 person-years of follow-up, there were 2548 incident cases of breast cancer. Compared with low levels of physical activity, high physical activity levels were inversely associated with risk for breast cancer (RR, 0.86; 95% confidence interval [CI], 0.78 - 0.96). There were inverse associations for ER+/PR+ (RR, 0.87; 95% CI, 0.75 - 1.00), ER+/PR- (RR, 0.67; 95% CI, 0.47 - 0.96), and ER-/PR- (RR, 0.80; 95% CI, 0.56 - 1.14) tumors.
Although further adjustment for body mass index decreased the overall association with breast cancer (RR, 0.91; 95% CI, 0.82 - 1.01) and for ER+/PR+ tumors (RR, 0.94; 95% CI, 0.81 - 1.08), there was no change for ER+/PR- tumors (RR, 0.66; 95% CI, 0.46 - 0.94).
Study limitations include physical activity measured as a single self-reported assessment at baseline, with no update during follow-up, lack of data on detailed aspects of physical activity, inability to calculate metabolic equivalents, information about ER/PR status obtained through multiple pathological laboratories rather than a single reference laboratory, and a predominantly white study population.
"Higher recreational physical activity might reduce the risk of postmenopausal breast cancer overall," the authors write. "Risk reduction varies by ER/PR status of the tumor, being most marked for ER+/PR- tumors, which, in general, have been associated with a clinically more aggressive tumor phenotype. If confirmed in additional studies, these results would suggest that additional mechanisms, besides an effect on body mass, may account for observed protective effects of physical activity in reducing breast cancer."
The National Cancer Institute supported this study in part. The authors have disclosed no relevant financial relationships.
Arch Intern Med. 2006;166:2478-2483.