NEW YORK - The number of moles a woman has may be tied to her risk of developing breast cancer, according to two new studies.
The studies don't prove that moles cause breast cancer or that women with a lot of moles will definitely get breast cancer. Instead, they suggest there may be a small genetic or hormonal link between the two.
"This shouldn't be a concern for women with moles, because we don't think the relationship is causal," said Marina Kvaskoff, the lead author of one of the new studies.
Kvaskoff is affiliated with INSERM - the French National Institute of Health and Medical Research - and the University of Paris 11.
Researchers suspected that moles, also known as nevi, and breast cancer might share links to certain hormones and genes. That would mean moles could be used to help predict a woman's breast cancer risk.
"We always need to discover more causes of cancer and breast cancer in particular," Kvaskoff said. "If more studies were to find nevi were associated with breast cancer risk, then nevi could become a risk marker for breast cancer risk."
In one of the studies, researchers led by Mingfeng Zhang at Brigham and Women's Hospital in Boston used data collected on 74,523 female nurses between 1986 and 2010 to measure women's breast cancer risk by the number of moles on their arms.
Women with no moles had about an 8.5 per cent chance of developing breast cancer during the study, compared to an 11.4 per cent chance of breast cancer among women with 15 or more moles on their left arm.
Among women who had already gone through menopause, Zhang and her colleagues found those with six or more moles had higher levels of estrogen and testosterone in their blood, compared to women without moles.
After adjusting their data to account for the differing hormone levels, the researchers found the link between moles and breast cancer disappeared.
In the other study that was led by Kvaskoff, researchers found that French women who reported having "very many moles" were 13 per cent more likely to develop breast cancer between 1990 and 2008 than women who had no moles. That study included 89,902 total women.
The association disappeared after the researchers adjusted the data to account for other breast cancer risk factors, including family history of breast cancer.
Kvaskoff said the findings suggest that the link between the number of moles a woman has and her risk of breast cancer could be genetic or hormonal. Her team did not have the data to take hormones into account, however.
The new studies, published in PLOS Medicine, are also limited because they mostly relied on white women. Additionally, one study asked women to report their own moles, which may be unreliable.
Kvaskoff said the magnitude of the associations the researchers found was small, which suggests moles may not be an important risk factor.
In an editorial accompanying the new studies, Barbara Fuhrman and Victor Cardenas from the University of Arkansas in Little Rock write that more research is needed.
They say that they hope additional studies will add information on the relationship between moles and breast cancer, and help with the assessment of breast cancer risk.
For now, Kvaskoff said the biggest risk of moles is skin cancer.
"Women in general should always get their moles checked for this reason," she said. "But it shouldn't be a concern with breast cancer."