Journal
CANCER EPIDEMIOLOGY BIOMARKERS & PREVENTION
Volume 21, Issue 7, Pages 1203-1212Publisher
AMER ASSOC CANCER RESEARCH
DOI: 10.1158/1055-9965.EPI-12-0310
Keywords
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Funding
- National Cancer Institute [R01-CA93881-01]
- Da Costa International Funds for Breast Cancer Prevention
- National Center for Research Resources (NCRR) [UL1 RR024146]
- NIH Roadmap for Medical Research
- Commission of Social Inequality in Cancer [SU08004]
- Albert Einstein Cancer Center
- National Heart, Lung, and Blood Institute
- NIH
- US Department of Health and Human Services [HHSN268201100046C, HHSN268201100001C, HHSN268201100002C, HHSN268201100003C, HHSN268201100004C, HHSN271201100004C]
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Background: Increased exposure to endogenous estrogen and/or insulin may partly explain the relationship of obesity, physical inactivity, and alcohol consumption and postmenopausal breast cancer. However, these potential mediating effects have not been formally quantified in a survival analysis setting. Methods: We combined data from two case-cohort studies based in the Women's Health Initiative-Observational Study with serum estradiol levels, one of which also had insulin levels. A total of 1,601 women (601 cases) aged 50 to 79 years who were not using hormone therapy at enrollment were included. Mediating effects were estimated by applying a new method based on the additive hazard model. Results: A five-unit increase in body mass index (BMI) was associated with 50.0 [95% confidence interval (CI), 23.2-76.6] extra cases per 100,000 women at-risk per year. Of these, 23.8% (95% CI, 2.9-68.4) could be attributed to estradiol and 65.8% (95% CI, 13.6-273.3) through insulin pathways. The mediating effect of estradiol was greater (48.8%; 95% CI, 18.8-161.1) for BMI when restricted to estrogen receptor positive (ER) cases. Consuming 7+ drinks/wk compared with abstinence was associated with 164.9 (95% CI, 45.8-284.9) breast cancer cases per 100,000, but no significant contribution from estradiol was found. The effect of alcohol on breast cancer was restricted to ER+ breast cancers. Conclusions: The relation of BMI with breast cancer was partly mediated through estradiol and, to a greater extent, through insulin. Impact: The findings provide support for evaluation of interventions to lower insulin and estrogen levels in overweight and obese postmenopausal women to reduce breast cancer risk. Cancer Epidemiol Biomarkers Prev; 21(7); 1203-12. (C)2012 AACR.
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