Women with a larger waist circumference may have a higher risk of postmenopausal breast cancer, but not beyond its contribution to body mass index, according to a recent study.

Researchers from the American Cancer Society found an association between body mass index and breast cancer, regardless of body shape. They failed to confirm previous findings that body shape itself is an independent risk factor for breast cancer.

Previous studies have linked abdominal obesity to a number of conditions, including heart disease, type II diabetes, and breast and other cancers.  Those studies have led to the theory that having an "apple shaped" body, with weight concentrated in the chest and torso, is riskier than having a "pear-shaped" body, with fat concentrated in the hips, thighs and buttocks.

For the study, researchers analyzed data from 28,965 women participating in the Cancer Prevention Study II. Among those women there were 1,088 invasive breast cancer cases diagnosed during a follow-up of nearly 12 years.

Investigators found a statistically significant positive association between waist circumference and postmenopausal breast cancer risk; however, when they adjusted for body mass index, the association disappeared.

"The message is that if you have a high BMI, regardless if you are pear or apple shaped, you are at higher risk of breast cancer," Dr. Mia Gaudet, lead researcher, said in a statement. "Most prior studies on this issue looked at BMI or at waist circumference, but had not looked at them together. This study brings some clarity to the association between obesity and risk of breast cancer."

Dr. Gaudet said the data could help women focus on what's important in what has been "a confusing array of potential risk factors for breast cancer."

"We know being overweight, particularly when the weight gain happened during adulthood, is one of the important modifiable risk factors for breast cancer in post-menopausal women," she said. "This new data indicates it's not what shape you are, it's what kind of shape you are in that probably ought to be their focus."