Asymmetrical Breasts May Raise Cancer Risk

Study finds odds for malignancy rise when breasts are of differing size

By Kathleen Doheny
HealthDay Reporter

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MONDAY, March 20 (HealthDay News) -- Asymmetry between a woman's breasts is normal, with few women having exactly the same-sized left and right breasts. But a new British study suggests that the greater the size difference between breasts, the higher a woman's risk of developing breast cancer.

"This is the first evidence of a possible link between breast asymmetry and predisposition to breast cancer," said lead researcher Diane Scutt, director of research in the School of Health Sciences at the University of Liverpool.

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Scutt's team published its findings Monday in the journal Breast Cancer Research.

The researchers calculated the breast asymmetry of 252 women free of breast disease when they got mammography but who later developed breast cancer. They then compared the findings to data on 252 healthy women of similar age.

Women who developed breast cancer had higher breast asymmetry than the healthy controls, the researchers found.

It's not yet known how much of a difference in size or volume matters, Scutt said, and it's not yet possible to quantify how much of a difference raises risk. "However, we can say that in the group we studied, the relative odds of developing breast cancer were 1.5 for every 100 milliliters difference [in size]. That is, risk increased by 50 percent for each 100 milliliters of asymmetry."

Why asymmetry might increase risk is not certain, Scutt said. It may be that women with symmetrical breasts can better tolerate hormonal ups and downs that occur during breast development. Exposure of breast tissue to estrogen is a known cancer risk factor.

"Breasts develop rapidly just prior to and during puberty," she said, "and the importance of estrogen in the development and growth of breasts is well-established. Symmetrical-breast development may well be an indicator of an individual's ability to tolerate 'disurptive' hormonal variation [that occurs during this developmental stage] while maintaining developmental stability."

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