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Breast Cancer Health Center

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Moles May Be Harbinger of Higher Breast Cancer Risk

Studies found that women with more moles on their arms had slightly higher chance of malignancies


The women were part of a long-term research project known as the Nurses' Health Study. Back in 1986 -- when the women were 40 to 65 years old -- they were asked to count the number of moles on their left arm.

Over the next 24 years, almost 5,500 women were diagnosed with breast cancer. And the odds, Han's team found, inched up with the number of moles the women had.

Among women with none, 8.5 percent developed breast cancer; that rate was 11.4 percent among women with 15 or more moles. Women with one to 14 moles fell in between, with almost 10 percent developing breast cancer.

Han's team considered a range of other factors -- including women's ages, lifestyle habits, weight, skin tone and sun exposure. (People with fair skin that sunburns easily typically have more moles.)

Even then, women with the most moles were 35 percent more likely to develop breast cancer than those with none.

The findings were similar in the second study, which followed nearly 90,000 French women aged 40 to 65. There was one key difference, though: Moles were linked to an increased risk only among women who developed breast cancer before menopause.

The reasons are not clear. But like Fuhrman, the researchers suggested hormones or genes could be involved.

In the American study, Han's team went a step further to try to tease out an explanation: They looked at hormone levels in a subgroup of postmenopausal women who'd given blood samples in the early years of the project.

And they found that, in fact, women with more moles tended to have higher levels of both estrogen and testosterone. What's more, the higher estrogen levels seemed to partly explain the connection between moles and breast cancer risk.

Still, while that "35 percent higher" risk sounds substantial, Fuhrman stressed that in statistical terms, the association was "weak." So, in real life, moles are likely to be a minor factor in any one woman's breast cancer risk.

Doctors already use so-called "risk models" to estimate whether a woman faces increased odds of breast cancer. Those models consider factors like family history of the cancer, and a woman's age at her first menstrual period -- a marker of lifetime estrogen exposure.

It's not clear, Fuhrman said, what a mole count would add to that.

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