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Asymmetrical Breasts May Raise Cancer Risk

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

MONDAY, March 20, 2006 (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.

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."

Another expert said that differences in size may or may not be noticeable, depending on breast size.

"One hundred milliliters is about a seven-tablespoon difference," said Dr. Paul Ian Tartter, senior attending surgeon at St. Luke's-Roosevelt Comprehensive Breast Center and associate professor of surgery at Columbia University College of Physicians and Surgeons, in New York City. The larger the overall breast size, the less noticeable that amount of asymmetry would be, he said.

He calls the new research "a thought-provoking study but it raises a lot more questions than answers." For instance, he said, "I would expect the larger breast to be at higher risk for breast cancer," because there is more breast tissue and more exposure to estrogen. "But they didn't find that."

The study needs to be duplicated, he said, and might not bear out.

Meanwhile, he said, women shouldn't be alarmed or concerned, noting that future studies may not replicate the link. And there is nothing a woman can do if this does turn out to be a risk, he noted. "It's not as if there is something here a woman [with very asymmetrical breasts] can change."

More information

For more on breast cancer, visit the American Cancer Society.

SOURCES: Dianne Scutt, Ph.D., director of research, School of Health Sciences, University of Liverpool, Liverpool, England; Paul Ian Tartter, M.D., senior attending, surgery, St. Luke's-Roosevelt Comprehensive Breast Center, and associate professor, surgery, Columbia University College of Physicians and Surgeons, New York City; March 20, 2006, Breast Cancer Research
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