Jun 11, 2014 08:11 AM EDT By Staff Reporter, UniversityHerald Reporter

Researchers from Indiana University, Harvard University and INSERM have discovered a novel predictor of breast cancer - Cutaneous nevi or moles.

Women, who have many moles on their skin, face heightened risk of developing breast cancer.

For the study, the researchers examined data from two cohorts - the Nurses' Health Study that followed 74,523 female nurses for 24 years, and the E3N Teachers' Study Cohort that observed 89,902 women for 18 years.

In the Nurses' Health Study, researchers asked participants to report the number of nevi >3mm on their left arm. Researchers found that women with 15 moles on their left arm were 35 per cent more likely to be diagnosed with breast cancer than those who reported no nevi.

The researchers believe that sex hormones might be playing a role in the link. In a sub-group of post-menopausal women, those with six or more moles were associated with higher levels of the hormones - oestrogen and testosterone - in the blood, than women who were mole-free.

Previous studies have already established a link between increased breast cancer risk and higher levels of sex hormones. In a 2013 study, Cancer Research UK scientists have identified the link in pre-menopausal women.

In the E3N Study, researchers asked participants to report whether they had no, a few, many, or very many moles. They found that women with "very many" nevi had 13 percent higher breast cancer risk than those with no nevi.

Researchers said that the studies do not establish the fact that nevi causes breast cancer. It highlights the role of sex hormones in nevi formation and development of breast cancer.

"Additional studies should be carried out to investigate melanocytic nevi and other cutaneous features in association with the risks of breast cancer and other estrogen-related proliferative diseases. It is our hope that this research will provide etiologic insights and test practical uses of nevi and related phenotypes for their potential utility in breast cancer risk assessment," the researchers said in a press release.

The finding is published in the journal Public Library Of Science Medicine.

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