In two separate studies with women, one in France and one in the U.S., the risk of breast cancer was increased for those with more moles. Researchers found in the U.S. study that women with 15 or more moles on one arm were 35% more likely to develop breast cancer than women who had no moles! The study was based on data gathered from 74,500 nurses who had been reporting the number of moles they had since 1986. From the time the study began until it ended almost 5,500 of the participants were diagnosed with breast cancer. In France a similar study was conducted that involved about 90,000 women. Researchers in this study also found a connection between the number of moles and breast cancer but in this case only when the woman was diagnosed before menopause. One theory is that estrogen, which is known to promote the growth of breast cancer, may also be promoting the growth of moles. While the results of these studies are only preliminary and are not able to be applied yet, they have prompted further questions on the association between moles and breast cancer.