Background: Triple-negative breast cancer, characterized by a lack of hormone receptor and HER2 expression, is associated with a particularly poor prognosis. Focusing on potentially modifiable breast cancer risk factors, we examined the relationship between body size, physical activity, and triple-negative disease risk.
Methods: Using data from 155,723 women enrolled in the Women's Health Initiative (median follow-up, 7.9 years), we assessed associations between baseline body mass index (BMI), BMI in earlier adulthood, waist and hip circumference, waist–hip ratio, recreational physical activity, and risk of triple-negative (n = 307) and estrogen receptor–positive (ER+, n = 2,610) breast cancers.
Results: Women in the highest versus lowest BMI quartile had 1.35-fold (95% CI, 0.92–1.99) and 1.39-fold (95% CI, 1.22–1.58) increased risks of triple-negative and ER+ breast cancers, respectively. Waist and hip circumferences were positively associated with risk of ER+ breast cancer (Ptrend = 0.01 for both measures) but were not associated with triple-negative breast cancer. Compared with women who reported no recreational physical activity, women in the highest activity tertile had similarly lower risks of triple-negative and ER+ breast cancers (HR = 0.77; 95% CI, 0.51–1.13; and HR = 0.85; 95% CI, 0.74–0.98, respectively).
Conclusions: Despite biological and clinical differences, triple-negative and ER+ breast cancers are similarly associated with BMI and recreational physical activity in postmenopausal women. The biological mechanisms underlying these similarities are uncertain and these modest associations require further investigation.
Impact: If confirmed, these results suggest potential ways postmenopausal women might modify their risk of both ER+ and triple-negative breast cancers. Cancer Epidemiol Biomarkers Prev; 20(3); 1–10. ©2011 AACR.
Note: Supplementary data for this article are available at Cancer Epidemiology, Biomarkers & Prevention Online (http://cebp.aacrjournals.org/).
- Received September 10, 2010.
- Revision received December 3, 2010.
- Accepted December 7, 2010.
- ©2011 American Association for Cancer Research.