Obese women with ER-positive/HER2-negative breast cancer have poorer survival rates

Obesity was associated with worse overall and disease-free survival in women with operable breast cancer treated with adjuvant chemotherapy. However, for the first time, researchers observed this finding in only a specific subset of patients - those with estrogen receptor (ER)-positive/human epidermal growth factor receptor 2 (HER2)-negative disease.

Researchers conducted a retrospective study to evaluate the effect of obesity on the outcomes of 3 Eastern Cooperative Oncology Group trials: E1199, E5188, and E3189. All 3 trials involved doxorubicin/cyclophosphamide and other agents.

They first evaluated the relationship between body mass index (BMI) and disease-free survival and overall survival in the E1199 trial. Results showed a nonsignificant trend toward worse disease-free survival and overall survival for the obese patients compared with others. However, after the data was evaluated by breast cancer subtype, obese women with ER and/or progesterone receptor (PR)-positive/HER2-negative disease had significantly worse disease-free survival and overall survival. The same effect was not seen in women with HER2-positive and triple-negative disease.

After this initial finding, researchers attempted to validate these findings in the 2 other trials, one of which included only ER-positive disease (E5188) and a second that included only ER-negative disease. The results held up in these studies; obesity was associated with worse outcomes in patients with ER-positive disease in the E5188 trial, but only in patients with ER-negative disease treated in the E3189 trial.

“We were surprised to find that there was no evidence that this finding played out in the other breast cancer subtypes,” said Joseph A. Sparano, MD, lead researcher and professor of medicine and women’s health at Albert Einstein Medical College of Medicine and associate chairman of the Department of Oncology at Montefiore Medical Center in Bronx, N.Y. “It’s mainly a phenomenon that we seem to be seeing in those with ER-positive/HER2-negative disease. Our results may be explained by the fact that obesity is associated with hyperinsulinemia, which may drive the growth of estrogen-dependent tumors.”