Obesity appears to increase the risk of breast cancer–related deaths by about one-third in premenopausal but, surprisingly, not postmenopausal women with estrogen receptor–positive disease, investigators report.
An analysis of pooled data on 80,000 patients enrolled in 70 clinical trials showed that among 60,000 patients with estrogen receptor (ER)-positive disease, body mass index (BMI) was associated with risk for breast cancer mortality in both pre- and perimenopausal women.
But after adjustment for patient factors and tumor characteristics, the association remained significant only for premenopausal women with ER-positive tumors, who had a 34% higher risk of dying from breast cancer, said Dr. Hongchao Pan, on behalf of colleagues in the Early Breast Cancer Trialists’ Collaborative Group.
“To our surprise, we found little independent adverse effects of obesity in the 40,000 postmenopausal women with ER-positive disease,” Dr. Pan said at a media briefing highlighting research to be presented at the annual meeting of the American Society of Clinical Oncology (ASCO) in Chicago, from May 30 through June 3.
There was also no apparent effect among women of any age with ER-negative tumors.
The findings suggest that the mechanisms by which obesity contributes to breast cancer prognosis are still unclear, Dr. Pan said.
The study was funded by Cancer Research UK, the Medical Research Council, and the British Heart Foundation. Dr. Pan, Dr. Yu, and Dr. Hudis reported having no relevant financial disclosures.
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