Previous reports have shown that obesity increases a woman’s risk of developing breast cancer - and now new research indicates that obesity continues to have a negative effect once breast cancer occurs.

Obese women with early-stage breast cancer are more likely than their normal-weight counterparts to have the cancer spread and to die of their cancer, according to findings presented Wednesday at the annual meeting of the American Society for Therapeutic Radiology and Oncology in Atlanta.

“Obesity is linked with the development of breast cancer,” lead author Dr. Penny R. Anderson, from the Fox Chase Cancer Center in Philadelphia, told Reuters Health. “Our study and others go on to show that breast cancer outcomes are less than optimal for women who are obese.”

The findings are based on a study of 2010 women with early breast cancer who underwent lumpectomy, removal of lymph nodes, and radiation therapy with or without chemotherapy.

The subjects were divided into normal weight, overweight, or obese groups. Women in the obese group were more likely to be older and postmenopausal than women in the other groups, the researchers note.

The size of the tumor and the number of involved lymph nodes did not differ between the groups. Still, the overall survival rate - 88 percent - at five years was slightly (but significantly) lower than the 92 percent rate seen in the other groups.

As to how obesity worsens breast cancer outcomes, Anderson said it’s unclear but may involve “effects on circulating estrogen levels and hormone metabolism.”