In women diagnosed with estrogen receptor (ER)-positive/HER2-negative breast cancer, obesity may contribute to poorer survival rates. These results were presented at the 2010 San Antonio Breast Cancer Symposium.

Obesity is a significant public health concern that can raise the risk of several serious health conditions, reduce quality of life, and increase medical expenses. Health risks associated with obesity include coronary heart disease, high blood pressure (hypertension), stroke, type 2 diabetes, certain types of cancer (including breast  cancer), and premature death. The CDC defines obesity as a body mass index (BMI) of 30% or greater. BMI is calculated from an individual’s weight and height.

In a retrospective study that included three trials from the Eastern Cooperative Group (trials E1199, E5188, and E3189), researchers evaluated the relationship between obesity and breast cancer outcomes.

In the first trial evaluated (E1199), researchers found that BMI appeared to be linked with disease-free and overall survival, with a non-significant worsening of survival among patients who were obese compared with non-obese patients. They then studied the data by breast cancer subtype and found that disease-free and overall survival was significantly worse among obese women who had ER-positive/HER2-negative disease. Obesity did not appear to affect survival among women with HER2-positive or triple-negative disease. Data from the other two trials validated these findings.

Obesity has been linked with worse outcomes in early breast cancer, but previous research has not isolated this relationship to a particular disease subtype. “We were surprised to find that there was no evidence that this finding played out in the other breast cancer subtypes—it’s mainly a phenomenon that we seem to be seeing [among] those with ER-positive/HER2-negative disease,” said one of the authors of the study. A possible explanation for the link between ER-positive/HER2-negative disease and obesity is the association of obesity with hyperinsulinemia (excess insulin in the blood), which may promote tumor growth in ER-positive breast cancer.

Additional research is planned into the relationship between obesity and outcomes in hormone-positive breast cancer, including efforts to identify causes of this association.

Reference: Sparano JA, Wang M, Martino S, et al. Obesity at diagnosis is associated with inferior outcomes in hormone receptor positive breast cancer. Presented at the 33rd annual San Antonio Breast Cancer Symposium, December 8-12, 2010. Abstract S2-1.

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