Obesity is associated with worse outcomes overall in early-stage breast cancer, researchers reported at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium, held Dec. 6-10, 2011.
Obesity was linked to shorter time to recurrence (TTR), disease-free survival (DFS) and overall survival (OS). The exception was treatment with endocrine therapy (mainly tamoxifen), in which obesity was associated with a protective effect.
"The findings add to the body of evidence indicating that obesity, in general, increases a patient's chance for having a worse prognosis," said lead researcher Sao Jiralerspong, M.D., Ph.D., an assistant professor of medicine at Baylor College of Medicine.
"Obesity is a probable risk factor for worse breast cancer outcomes, and ours is the latest study to suggest it has an effect on treatment outcome as well," Jiralerspong said.
Using data from the Lester and Sue Smith Breast Center at Baylor, Jiralerspong and colleagues examined the link between weight and treatment modality in 4,368 patients treated between 1970 and 1995.
For the group as a whole, data revealed that overweight patients had similar outcomes to normal-weight patients, but obese patients had an increased risk for worse TTR, DFS and OS.
Among patients who received no adjuvant chemotherapy or endocrine therapy, there was a trend for worse survival outcomes in obese patients compared with normal-weight patients.
Obese patients who received chemotherapy fared significantly worse compared with normal-weight patients, "with the magnitude of this effect approaching that of the degree of benefit expected from chemotherapy," Jiralerspong said.
In contrast, overweight patients who received endocrine therapy, predominantly tamoxifen, fared significantly better compared with normal-weight patients.
"Finding that overweight patients have a better outcome than normal-weight patients after tamoxifen treatment is surprising. We are examining the possible reasons for this," Jiralerspong said.
He said that obesity could contribute to worse outcomes because of biological factors associated with excess weight, such as higher blood insulin and estrogen levels, inflammation and growth factors secreted by fat cells. But Jiralerspong also added that more research is needed to understand the effect of body mass on adjuvant treatment because of the unexpected findings and because additional agents are in use today compared with the time period studied.