Obesity Substantially Increases Breast Cancer Mortality Only in Women With Premenopausal Estrogen Receptor–Positive Disease
A new study of 80,000 women with early breast cancer in 70 clinical trials finds that obesity is associated with a 34% higher risk of breast cancer–related death only among the 20,000 premenopausal women who had estrogen receptor–positive disease. Obesity had little effect in postmenopausal estrogen receptor–positive disease or in estrogen receptor–negative disease. The study findings were presented today at a presscast in advance of the 2014 ASCO Annual Meeting (Abstract 503).
“Obesity substantially increases blood estrogen levels only in postmenopausal women, so we were surprised to find that obesity adversely impacted outcomes only in premenopausal women,” said Hongchao Pan, PhD, a researcher at the University of Oxford in the United Kingdom. Dr. Pan continued, “This means we don’t understand the main biological mechanisms by which obesity affects prognosis.”
Study Details
This Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) study compared records from women who received the same treatment in the same clinical trial. Body-mass index (BMI) was used to define normal weight, overweight, and obesity (20–25, 25–30 and ≥ 30 kg/m2). To assess the independent effects of BMI on prognosis, the researchers adjusted the findings for tumor characteristics such as size and nodal spread, and for any differences in treatment.
Among the 20,000 premenopausal patients with estrogen receptor–positive disease, the breast cancer mortality rate was one-third higher in obese women than in women of normal weight. This would, for example, change a 10-year breast cancer mortality risk of 15% into a 10-year risk of 20%.
In contrast, obesity had little effect on breast cancer outcome either among the 40,000 postmenopausal women with estrogen receptor–positive disease or among the 20,000 with estrogen receptor–negative disease.
Obesity and Cancer Management
“This study is part of the growing body of evidence showing that patients who are obese generally fare worse with cancer—in this case, younger women with breast cancer,” explained ASCO President Clifford A. Hudis, MD, FACP. “With some two-thirds of our nation’s adult population now obese or overweight, there’s simply no avoiding obesity as a complicating factor in cancer care. ASCO is working to support physicians and patients in addressing this challenge, and we urge researchers to examine new strategies for reducing obesity’s cancer-related toll."
This week, ASCO released two new resources to help physicians manage the complications of obesity in patients with cancer: “Obesity and Cancer: A Guide for Oncology Providers,” available at www.asco.org/obesity, and a complementary guide for patients, available at www.cancer.net/obesity.
The study was funded by Cancer Research UK, the Medical Research Council, and the British Heart Foundation. The study authors reported no potential conflicts of interest.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
