However, after evaluating these data 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 was seen in the E1199 trial, the research team attempted to validate these findings in two 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 two other 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.

"If validated in other studies, this finding provides strong rationale for trying to identify potential causes, and prospectively evaluate intervention strategies designed to reduce their risk of recurrence," Sparano said.

The researchers plan additional studies to evaluate the relationship between obesity and tumor gene expression, and to identify other host factors that may be associated with recurrence, such as insulin and other growth-factor levels.

Source: CTRC-AACR San Antonio Breast Cancer Symposium