"Obesity is clearly associated with an increased risk, and even women who were not obese but overweight tend to have a high risk," Sparano said. However, he said he can't pinpoint a weight threshold at which the risk begins.
It's important to note that although a link between recurrence and excess weight was detected, the research does not show cause and effect.
Commenting on the study, Dr. Bette Caan, a senior research scientist at the Kaiser Permanente Division of Research in Oakland, Calif., said the researchers were able to address some of the shortcomings of previous studies.
"To me the big news is that it is showing obesity is only related to one subtype," Caan said. "It's the most common subtype.
"Breast cancer is not one disease but several diseases," she added.
What is not yet known, agreed Sparano and Caan, is whether reducing weight after cancer treatment might reduce the risk of recurrence or death.
Studies looking at the effect of reducing dietary fat on the risk of recurrence in obese women have come up with conflicting results. In one study, reduced fat didn't lead to weight loss or reduced recurrence.
More study is needed, these experts say. It might turn out that weight loss only plays a role in reducing recurrence risk for some women, Caan said.
To learn about obesity and breast cancer, visit the U.S. National Cancer Institute.
SOURCES: Joseph Sparano, M.D., associate chairman, oncology, Montefiore Medical Center, and professor of medicine, Albert Einstein College of Medicine, New York City; Bette Caan, Dr.P.H., M.P.H., senior research scientist, Kaiser Permanente Division of Research, Oakland, Calif.; Aug. 27, 2012, online,
All rights reserved