The number of moles located on a woman’s left arm may the simplest way to predict whether a she will get breast cancer has been demonstrated in two new studies. The first was lead by researcher Marina Kvaskoff, PhD, a fellow at Brigham & Women’s Hospital and Harvard Medical School who’s E3N Teachers Study Cohort tracked more than 89,900 women over an 18-year period. The second, known as the Nurses’ Health Study in the United States, followed 74,523 women for 24 years. What they both found was that “women with 15 or more moles on their left arm were up to 35% more likely to develop breast cancer, compared to women with no moles on their arm.”
“We don’t think that nevi actually cause breast cancer, but there could be several reasons for the association we observed, including genetic and hormonal factors,” stated Kvaskoff.
Her study suggested that genes could be a key player in risk for both conditions, while the Nurses’ Health Study linked the number of moles on a woman’s arm to higher blood levels of the sex hormones estrogen and testosterone, which in turn may contribute to breast cancer risk. “We know that having a large number of common nevi is the number one risk factor for melanoma, and that there’s a link between melanoma and breast cancer, and earlier studies have connected skin moles to increased risk for a number of other disorders influenced by hormones, including endometriosis (a condition in which tissue similar to the lining of the uterus grows outside of the pelvis), uterine fibroids, and thyroid disease,” she continued.
It was also noted that hormones during pregnancy have a tendency to increase the size and deepen the color of moles. Meanwhile, researchers involved with the Nurses Study found that postmenopausal women with upwards of 6 moles had “higher blood levels of estrogen and testosterone, compared to women without any,” and led them to surmise that “that moles may be a marker of higher hormonal levels, which in turn may predict breast cancer risk.”