The number of moles a woman has may be tied to her risk of developing breast cancer, according to two new studies.
Despite their discovery, however, the new studies, published in PLOS Medicine, do not necessarily 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.
Researchers suspected that moles, also known as nevi, and breast cancer might share links to certain hormones and genes, meaning 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.”
One study 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 percent chance of developing breast cancer, compared to an 11.4 percent chance of breast cancer among women with 15 or more moles on their left arm. Among women who had already gone through menopause, researchers 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.
Experts say the studies are also limited because they mostly relied on White women. Moreover, one study asked women to report their own moles, which may be unreliable.
Researchers 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, however, 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.”