FRIDAY, March 23 (HealthDay News) -- Overweight and obese breast cancer patients are at increased risk for recurrence of the disease, a new study finds.

The findings -- which held true even though chemotherapy doses were adjusted for weight -- provide further evidence that lifestyle factors can influence cancer patient outcomes, according to Dr. Jennifer Ligibel, a medical oncologist at the Dana-Farber Cancer Institute in Boston, and an associate professor at Harvard Medical School.

She and her colleagues analyzed data collected from 1,909 breast cancer patients. Of those women, about 1 percent were underweight, 33 percent were normal weight, 33 percent were overweight and 33 percent were obese.

The researchers examined the link between body-mass index (a measure of body fat based on weight and height) and relapse-free survival and overall survival. The findings are slated for presentation Friday at the European Breast Cancer Conference in Vienna.

"Several other studies have shown that being overweight or obese at the time that a woman is diagnosed with breast cancer is linked to a higher risk of recurrence. However, questions have been raised in the past whether obese women were receiving relatively lower doses of chemotherapy due to their weight. Our study mandated that each patient received a chemotherapy dose adjusted to her weight, so these results suggest that treatment factors are not responsible for the differences in recurrence rates seen in heavier women," Ligibel said in a conference news release.

"We found that BMI was related to both relapse-free survival and overall survival; for example, the 10-year relapse-free survival of a patient who was overweight was 70 percent; compared with 65 percent for one who was obese," she noted.

Ligibel concluded: "Obesity is a modifiable factor, and although there is not yet enough evidence to say with certainty that losing weight or exercising more regularly will decrease the risk of breast cancer recurrence, there are consistent links between lifestyle factors such as diet, weight and physical activity patterns and breast cancer prognosis. If future studies show that making changes in lifestyle behaviors for women with early breast cancer will improve survival rates, then lifestyle interventions may one day become a standard part of breast cancer care."

According to conference chair David Cameron, a professor at the University of Edinburgh in Scotland, these are important findings for women with breast cancer but "we need to recognize that the reason overweight women have poorer outcomes is not clear," he said in the news release.

"There are a lot of health reasons why overweight women should try and get back to a normal weight, but this is not always easy, and as the authors acknowledge, we don't yet know that losing weight after a breast cancer diagnosis will make a difference," he noted.

Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

The U.S. National Cancer Institute has more about breast cancer.