Breast asymmetry and breast cancer

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March 20, 2006 -- The difference in the size of a woman's right and left breast may help predict her risk for developing breast cancer.

Few women have perfectly symmetrical breasts, but the intriguing early research from the U.K. suggests that larger difference in size is an independent risk factor for the disease.

In a study published Monday in the journal Breast Cancer Research, researchers reported that each 3.38 ounce increase in breast asymmetry, as measured by mammography, predicted a 50% increase in breast cancer risk.

The average breast size of the 504 women in the study was 16.9 ounces and the average asymmetry was 1.7 ounces to 2.03 ounces, says Diane Scutt, PhD, one of the study researchers.

Only one woman in the study had breasts that were exactly symmetrical.

"This early work is very encouraging," Scutt tells WebMD. "It certainly suggests that breast asymmetry could be a good independent predictor of breast cancer risk."

Balanced Evidence

Scutt and colleagues studied mammograms from 252 women free of breast cancer at the time of breast imaging but who developed the disease later on. An equal number of women with normal mammograms from women who did not develop breast cancer were also examined.

The finding that women who later developed breast cancer had more asymmetry than those who did not is consistent with previous studies by the same researchers comparing mammograms from breast cancer patients and nonpatients.

The researchers hope to confirm the findings by examining mammograms from 13,000 women who were free of breast cancer when they entered a study on menopause 25 years ago. Differences in breast size will be compared between women who later developed breast cancer and those who did not.

Even if those findings suggest a strong link between breast asymmetry and breast cancer, Scutt says it is just one of many traits that influence breast cancer risk.

More Study Needed

If breast asymmetry is a factor in risk then estrogen may explain why.

"Our previous work seems to indicate that estrogen plays a part in asymmetry," Scutt says, "But the short answer is that we need to do more work to figure this out."

American Cancer Society spokesman Len Lichtenfeld, MD, FACP, agrees. He adds that it isn't likely that breast asymmetry will be used to predict breast cancer risk anytime soon.

"We have identified a variety of characteristics that are known to influence risk," he tells WebMD. "Family history, a woman's age, her reproductive history, and other factors play a role. These new findings are interesting, but they are very preliminary."