A theory regarding the correlation is that estrogen is the common denominator of moles and breast cancer. Estrogen is known to fuel the growth and spread of many breast tumors, and is thought to influence mole growth as well.
In the study, researchers analyzed data on more than 74,500 female nurses who participated in a long-term research project called the Nurses’ Health Study that began in 1986 when the women were ages 40 to 65. Participants were asked to keep track of the number of moles on their left arm.
Over the next 24 years, nearly 5,500 of the women were diagnosed with breast cancer. More than 8 percent of the women with no moles developed breast cancer, while 10 percent of those with one to 14 moles did. Among women with 15 or more moles, 11.4 percent were diagnosed with breast cancer.
In the study overall, women with the most moles were 35 percent more likely to develop breast cancer than those with none.
The French study followed nearly 90,000 French women from ages 40 to 65. There was a unique difference in this study compared with the U.S. study findings: The French team found links between moles and an increased risk of breast cancer only among women who developed it before menopause.
“Our findings indeed suggest that nevi share genetic and/or hormonal characteristics with breast cancer,” the study’s lead author, Marie-Christine Boutron-Ruault, M.D., of Institut Gustave Roussy, Paris, tells Dermatology Times. “However, our and Dr. Zhang’s studies are the first to report such associations, and they were of small magnitude, especially compared with associations of nevus count with cutaneous melanoma.
“These findings are thus too preliminary to have implications in terms of clinical practice and screening, but they should prompt further research to understand potential underlying mechanisms.”