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Obesity Ups Death Risk in Premenopausal Patients with ER-Positive, but Not ER-Negative, Breast Cancer

June 2014, Vol 5, No 5

Chicago, IL—Obesity increased the risk for breast cancer–associated death in premenopausal patients with estrogen receptor (ER)-positive breast cancer, had little effect in postmenopausal women with ER-positive disease, and had no effect in patients with ER-negative disease, according to results of a large study of 80,000 women with early breast cancer that were reported at the 2014 American Society of Clinical Oncology (ASCO) meeting.

In premenopausal patients with ER-positive breast cancer, obesity increased the risk of death by 34%. Surprisingly, this was not the case in postmenopausal women.

Obesity is a well-known public health problem and is associated with an increased risk for breast cancer, as well as a long list of other potential adverse effects on health.

“It has been shown that obesity increases the risk of developing cancer, and this study says it increases the risk of poor outcome once you have cancer if you are premenopausal and have ER-positive breast cancer,” said lead investigator Hongchao Pan, PhD, Medical Research Council Senior Research Fellow, Clinical Trial Service Unit and Epidemiological Studies Unit, University of Oxford, United Kingdom, at a press briefing.

The results of the study surprised Dr Pan and his colleagues, who expected to see an increased mortality risk in patients with pre- and postmenopausal ER-positive breast cancer. “These paradoxical findings show that we have an incomplete understanding of the mechanisms associated with obesity and breast cancer prognosis,” Dr Pan noted.

“Obesity is a major challenge, and trends suggest that it will replace tobacco as our leading public health problem. With some two-thirds of adults in the United States now obese or overweight, there is no avoiding obesity as a complicating factor in cancer care. ASCO is working to support physicians and patients who need to lose weight. New strategies are needed to address this challenge,” stated ASCO President Clifford A. Hudis, MD, Chief, Breast Cancer Medicine Service, Memorial Sloan Kettering Cancer Center, New York, at a press briefing.

Study Details
The study was conducted by the Early Breast Cancer Trialists’ Collaborative Group and was based on the records of 80,000 women enrolled in 70 clinical trials. Obesity was defined as a body mass index (BMI) of ?30 kg/m2, overweight as a BMI of 25 kg/m2 to 30 kg/m2, and normal weight as 20 kg/m2 to 25 kg/m2.

Data were collected on ER status, menopausal status, and cancer recurrence, and the findings were adjusted for tumor characteristics, including size and nodal status, and for any differences in treatment.

A Cox regression analysis that was undertaken to compare the effects of obesity on breast cancer mortality in obese versus normal-weight women showed that obesity was a significant and independent factor associated with breast cancer death in 20,000 premenopausal ER-positive women (relative risk [RR], 1.34 [95% confidence interval (CI), 1.22-1.47]; 2-sided P value <.001).

Little effect of obesity was observed in the 40,000 postmenopausal women with ER-positive disease (RR, 1.06; 95% CI, 0.99-1.14), and no effect was found in the 20,000 women with ER-negative disease (RR, 1; 95% CI, 0.93-1.08).

At 10 years, the breast cancer–related mortality rate was 21.5% in obese women and 16.6% in normal-weight women, a difference of approximately 5%.

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