Body Size, Physical Activity, and Breast Cancer Hormone Receptor Status: Results from Two Case-Control Studies

Body Size, Physical Activity, and Breast Cancer Hormone Receptor Status: Results from Two Case-Control Studies1

Research and Evaluation Department, Kaiser Permanente Medical Care Program, Southern California, Pasadena, California 91188 [S. M. E.], and Department of Preventive Medicine, University of Southern California/Norris Comprehensive Cancer Center, Los Angeles, California 90033 [S. M. E., R. K. R., A. P-H., C. L. C., L. B.]

Abstract

We evaluated whether our previous reports of increased postmenopausal breast cancer risk with higher body mass index (BMI) or of reduced premenopausal and postmenopausal breast cancer risk with higher physical activity levels varied according to the tumor’s estrogen receptor (ER) and progesterone receptor (PR) status. Participants enrolled in either of two population-based case-control studies in Los Angeles County, California: one of premenopausal women (ages ≤40 years), and one of postmenopausal women (ages 55–64 years). Case participants were diagnosed for the first time with in situ or invasive breast cancer from 7/1/83 through 12/31/88 (premenopausal women) or from 3/1/87 through 12/31/89 (postmenopausal women). Joint ER/PR status was collected for 424 premenopausal and 760 postmenopausal case participants. The analysis included 714 premenopausal and 1091 postmenopausal age-matched, race-matched (white or Hispanic), parity-matched (premenopausal women only), and residential neighborhood-matched control participants.

Among the postmenopausal women, obesity was associated with an increased odds of ER+/PR+ breast cancer (odds ratio, 2.45 for women in the highest versus the lowest body mass index quartile; 95% confidence interval, 1.73–3.47). Body mass index was associated with neither ER−/PR− tumors among the postmenopausal women nor with any ER/PR subgroup among the premenopausal women. For both premenopausal and postmenopausal women, higher recreational physical activity levels (≥17.6 MET-hours/week versus no activity) were associated with a 30–60% reduction in risk of nearly all ER/PR subtypes, although the associations were generally of borderline statistical significance. Examining these potentially modifiable breast cancer risk factors by tumor ER and PR status may provide us with greater insight into breast cancer etiology and the mechanisms underlying the risk factor associations.

Footnotes

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↵1 Initial data collection for the two case-control studies was supported by USPHS Grants CA17054 and CA44546 and Contract N01-CN25404 from the National Cancer Institute, NIH, Department of Health and Human Services, and by the California Public Health Foundation Subcontract 050-F-8709, which is supported by the California Department of Health Services as part of its statewide cancer-reporting program mandated by Health and Safety Code Sections 210 and 211.3. The ideas and opinions expressed herein are those of the authors, and no endorsement by the state of California, Department of Health Services, or the California Public Health Foundation is intended or should be inferred. S. M. E. was supported by funds from the California Breast Cancer Research Program of the University of California, Grants 1FB-0341 and 3FB-0097.
↵2 To whom requests for reprints should be addressed, at Department of Research and Evaluation, Kaiser Permanente Medical Care Program, 100 South Los Robles Avenue, Second Floor, Pasadena, CA 91188. Phone: (626) 564-3201; Fax (626) 564-3430; E-mail: Shelley.M.Enger{at}kp.org
↵3 The abbreviations used are: ER, estrogen receptor; PR, progesterone receptor; OR, odds ratio, CI, confidence interval; BMI, body mass index; CSP, Cancer Surveillance Program.
- Accepted April 24, 1900.
- Received August 10, 1999.
- Revision received March 16, 1900.