Number of skin moles tied to breast cancer risk

Women who have many moles on their skin are slightly more prone to breast cancer than those without them, two studies find. Skin moles, benign clumps of pigmentation-producing cells called melanocytes, might arise from high levels of hormones in women’s blood, which also could facilitate tumor growth, one of the studies suggests.

Although the appearance of moles can be influenced by an individual’s genetics, the new studies and earlier work suggest that exposure to estrogen plays a role, too, says Barbara Fuhrman, an epidemiologist at the University of Arkansas for Medical Sciences in Little Rock. Like cells in the breast and elsewhere, melanocytes have receptor proteins that estrogen can bind to, triggering cell activities that include growth.

High mole counts have been linked to uterine tissue overgrowth called endometriosis and to a higher risk of melanoma, the dangerous kind of skin cancer. The new studies, appearing in the June PLOS Medicine, are the first large analyses to show a connection between moles and breast cancer.

In one study, scientists asked nearly 90,000 women in France, mostly teachers, for a self-assessment of their skin moles. Those who described themselves as having “very many” moles were 13 percent more likely to develop breast cancer during a median follow-up of 18 years compared with those reporting no moles.

In the other study, epidemiologist Jiali Han of Indiana University in Indianapolis led a team that analyzed data from nearly 75,000 female nurses whose health has been monitored for decades. At the outset of the study, each nurse had been asked to count the moles on her left arm. During 24 years of follow-up, about 8.5 percent of women without any moles and 11.4 percent of those with 15 or more developed breast cancer —an increase of roughly one-third. The researchers also found that estrogen levels in women who had six or more moles on the arm were nearly 46 percent higher than in women with no moles.

French study coauthor Marie-Christine Boutron-Ruault of INSERM, the French National Institute of Health and Medical Research in Paris, allows that the link between moles themselves and breast cancer is “indirect.” A woman’s breast cancer risk is also affected by her family history, age at first menstruation, number of pregnancies, genetics and other factors, she notes. But she says that the potential addition of moles to the list bolsters a hormone connection. In breast cancer and endometriosis, estrogen contributes to unwanted tissue growth, and both are now linked with a high mole count. “All this points to a sort of common background,” she says. “This should prompt research into this field.”