Women with asymmetrical breasts may be more likely to develop breast cancer, research suggests.
Mammography can pick up changes in the breast
A University of Liverpool team compared mammograms of 252 women who went on to develop breast cancer with a similar number from women who stayed healthy.
The study in the journal Breast Cancer Research found the relative odds of getting cancer went up 50% for each 100ml increase in breast asymmetry.
But the authors warned breast cancer risk depended on a number of factors.
Humans, in common with most other vertebrates, tend to show bilateral symmetry - meaning that the two halves of the body are basically symmetrical.
However, perfect symmetry may be disturbed by factors such as uneven secretion of hormones.
Thus researchers believe that asymmetry is a sign that development of the body is not as stable as it might be.
Certainly, humans seem to be pick up on this on a sub-conscious level. Studies have shown that symmetrical people are constantly rated as more attractive.
The latest study appears to add to this theory by suggesting that people with asymmetrical breasts are more likely to be prone to developmental disturbances that ultimately can lead to cancer.
Writing in the journal, the researchers said: "Asymmetrical breasts could prove to be reliable indicators of future breast disease in women and this factor should be considered in a woman's risk profile."
Lead researcher Dr Diane Scutt told the BBC News website the average female breast in the study was about 500ml in size, so a variation of 100ml was quite big.
She added that almost all women had some degree of breast asymmetry - just one woman who took part in the study had perfectly symmetrical breasts.
She said: "Breast asymmetry should not be considered in isolation, it is important to consider a woman's entire risk profile before assessing her breast cancer risk."
More work needed
Maria Leadbeater, of the charity Breast Cancer Care, said the results were not conclusive, and that more work was needed to establish whether there was a link.
She said: "There are many causes of breast asymmetry, and for many women having slightly different shaped breasts is perfectly normal.
"However, if your breasts are normally close in size and you notice them becoming asymmetrical it is important to get this change checked out with your doctor.
"This is all part of being breast aware, meaning knowing how your breasts look and feel so you can report any changes promptly."
Dr Sarah Rawlings, of Breakthrough Breast Cancer, said it was too early to say whether breast asymmetry was linked to cancer.
"Other factors, such as starting periods early, may have had an influence and were present more often in those women who went on to develop breast cancer in this study."
Professor Stephen Duffy, professor of screening at Cancer Research UK, said it was known that the left breast tended to be very slightly larger.
Many studies had reported a slightly larger proportion of breast cancers to occur in the left breast (around 51%).
He said: "This study confirms the first observation but not the second.
"It also finds that having one breast substantially larger than the other is associated with increased risk of breast cancer.
"But this increase in risk is small compared with other risk factors such as breast density.
"So it does not have immediate implications for prevention or screening."