This Article  • Full text  • PDF  • Send to a friend  • Save in My Folder  • Save to citation manager  • Permissions  Citing Articles  • Citation map  • Citing articles on HighWire  • Citing articles on Web of Science (14)  • Contact me when this article is cited  Related Content  • Related letters  • Similar articles in this journal  Topic Collections  • Oncology  • Breast Cancer  • Women's Health  • Women's Health, Other  • Alert me on articles by topic  Social Bookmarking   What's this?

Aditya Bardia, MD, MPH; Lynn C. Hartmann, MD; Celine M. Vachon, PhD; Robert A. Vierkant, MS; Alice H. Wang, BS; Janet E. Olson, PhD; Thomas A. Sellers, PhD; James R. Cerhan, MD, PhD

Arch Intern Med. 2006;166:2478-2483.

Background  Physical activity is a potentially modifiable breast cancer risk factor. 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.

Methods  The Iowa Women's Health Study is a prospective cohort study of 41 836 postmenopausal women. Recreational physical activity was self-reported on the baseline questionnaire, and 3 levels (high, medium, and low) were defined. Breast cancer incidence and ER/PR status, through 18 years of follow-up, were ascertained by linkage with the Iowa Surveillance, Epidemiology, and End Results Cancer Registry. Cox proportional hazards models were used to estimate multivariate relative risks (RRs) and 95% confidence intervals (CIs) of breast cancer, adjusting for other breast cancer risk factors.

Results  During 554 819 person-years of follow-up, 2548 incident cases of breast cancer were observed. Compared with low physical activity, high physical activity levels were inversely associated with risk of breast cancer (RR, 0.86; 95% CI, 0.78-0.96), and there were inverse associations for ER-positive (ER⁺)/PR-positive (RR, 0.87; 95% CI, 0.75-1.00), ER⁺/PR-negative (PR^–) (RR, 0.67; 95% CI, 0.47-0.96), and ER-negative/PR^– (RR, 0.80; 95% CI, 0.56-1.14) tumors. Further adjustment for body mass index attenuated the overall association with breast cancer (RR, 0.91; 95% CI, 0.82-1.01) and for ER⁺/PR-positive tumors (RR, 0.94; 95% CI, 0.81-1.08), while there was no change for ER⁺/PR^– tumors (RR, 0.66; 95% CI, 0.46-0.94).

Conclusions  Higher recreational physical activity might reduce the risk of postmenopausal breast cancer overall. 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.

Author Affiliations: Departments of Internal Medicine (Dr Bardia), Medical Oncology (Dr Hartmann), and Health Sciences Research (Drs Vachon, Olson, and Cerhan, Mr Vierkant, and Ms Wang), Mayo Clinic College of Medicine, Rochester, Minn; and Division of Cancer Prevention and Control, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Fla (Dr Sellers).

CiteULike    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter     What's this?

RELATED LETTERS

The Number Needed to Be Exposed: A Potential Use for Quantifying the Strength of an Individual Risk Factor Including a Protective Factor in a Cohort Study
Huai yong Cheng
Arch Intern Med. 2007;167(15):1690.
EXTRACT | FULL TEXT  

The Number Needed to Be Exposed: A Potential Use for Quantifying the Strength of an Individual Risk Factor Including a Protective Factor in a Cohort Study—Reply
James R. Cerhan, Aditya Bardia, Robert A. Vierkant, and Celine M. Vachon
Arch Intern Med. 2007;167(15):1690-1691.
EXTRACT | FULL TEXT  

THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES

Prevention of Breast Cancer in Postmenopausal Women: Approaches to Estimating and Reducing Risk
Cummings et al.
JNCI J Natl Cancer Inst 2009;101:384-398.
ABSTRACT | FULL TEXT  

Physical Activity and Postmenopausal Breast Cancer Risk in the NIH-AARP Diet and Health Study
Peters et al.
Cancer Epidemiol. Biomarkers Prev. 2009;18:289-296.
ABSTRACT | FULL TEXT  

Physical Activity and Postmenopausal Breast Cancer: Effect Modification by Breast Cancer Subtypes and Effective Periods in Life
Schmidt et al.
Cancer Epidemiol. Biomarkers Prev. 2008;17:3402-3410.
ABSTRACT | FULL TEXT  

Effect of Physical Activity on Breast Cancer Risk: Findings of the Japan Collaborative Cohort Study
Suzuki et al.
Cancer Epidemiol. Biomarkers Prev. 2008;17:3396-3401.
ABSTRACT | FULL TEXT  

Physical activity and breast cancer risk: impact of timing, type and dose of activity and population subgroup effects
Friedenreich and Cust
Br. J. Sports. Med. 2008;42:636-647.
ABSTRACT | FULL TEXT  

The Number Needed to Be Exposed: A Potential Use for Quantifying the Strength of an Individual Risk Factor Including a Protective Factor in a Cohort Study
Cheng
Arch Intern Med 2007;167:1690-1690.
FULL TEXT  

The Number Needed to Be Exposed: A Potential Use for Quantifying the Strength of an Individual Risk Factor Including a Protective Factor in a Cohort Study Reply
Cerhan et al.
Arch Intern Med 2007;167:1690-1691.
FULL TEXT  

Exercise and Breast Cancer Risk Revisited
JWatch Women's Health 2007;2007:3-3.
FULL TEXT