Common moles (doctors call them nevi) are small growths on your skin that are usually pink, tan, or brown and have a distinct edge. Moles develop when pigment cells grow in clusters. Most adults have about 10 to 40 moles, mostly above the waist on parts of the body that are exposed to the sun. While common moles aren’t cancerous, people who have more than 50 common moles have a higher risk of developing skin cancer.
Now two studies seem to have found a link between moles and breast cancer. Both studies suggest that women with more moles are more likely to develop breast cancer.
Both studies were published in the June 10, 2014 issue of the PLoS Medicine. Read the abstracts of:
- “Association between Melanocytic Nevi and Risk of Breast Diseases: The French E3N Prospective Cohort”
- "Association between Cutaneous Nevi and Breast Cancer in the Nurses’ Health Study: A Prospective Cohort Study”
Both of these studies were prospective studies. A prospective study follows a group of similar people who are different in terms of the factors that are being studied to see how the factors affect rates of a certain outcome.
In the French E3N study, the researchers followed 89,902 women to see if the number of moles they had were linked to breast cancer risk. The women in the study were ages 40 to 65 and were followed from June 1990 to June 2008. Most of the women in the study were school teachers.
At the beginning of the study, the researchers asked the women if they had:
- no moles
- a few moles
- many moles
- very many moles
and other questions about their lifestyle and medical history.
Throughout the study, the researchers regularly reviewed the women’s medical records.
During the study, 5,956 breast cancers were diagnosed in the women.
Overall, women who had “very many” moles had a 13% higher risk of breast cancer than women who had no moles. This difference was significant, which means it was probably because of the difference in the number of moles and not just due to chance.
Still, when the researchers factored in any personal history of benign breast disease or family history of breast cancer (both of which increase breast cancer risk), the link between moles and higher breast cancer risk wasn’t significant, which means it could have just happened by chance.
The French researchers then did another analysis of the information, this time only looking at premenopausal women. Even when the researchers factored in any history of benign breast disease or breast cancer, the link between having very many moles and a higher risk of breast cancer stayed significant, which means it was likely due to the difference in the number of moles.
So the French E3N study suggests that premenopausal women with very many moles may have a higher risk of breast cancer.
In the Nurses’ Health Study, researchers followed 74,523 white female nurses from 1986 to 2010. At the beginning of the study, all the women reported how many moles they had on their left arm.
Over the 24 years of the study, 5,483 invasive breast cancers were diagnosed in the women.
After the researchers factored in any other breast cancer risk factors, they found that compared to women with no moles, women with higher numbers of moles had a higher risk of breast cancer:
- women with five or fewer moles had a 4% higher risk
- women with six to 14 moles had a 15% higher risk
- women with 15 or more moles had a 35% higher risk
The researchers also found that postmenopausal women with six or more moles had higher blood levels of estrogen and testosterone than women with no moles.
The researchers then did another analysis that took into account the women’s estrogen and testosterone levels and found that any links between the number of moles and breast cancer risk disappeared.
Researchers think that the hormones estrogen and progesterone, which can affect breast cancer development, also affect whether moles develop or not. So while moles don’t cause breast cancer, having more moles may indicate that a woman has higher blood levels of estrogen.
The results of these studies suggest that the number of moles a woman has could some day be used to help calculate breast cancer risk. Still, it’s not clear if this information would be more helpful than the way risk is calculated right now based on established risk factors, including family history, age, breast density, pregnancy history, breastfeeding history, and genetics.
Every woman wants to know what she can do to lower her risk of breast cancer. Some of the factors associated with breast cancer -- being a woman, your age, and your genetics, for example -- can't be changed. Other factors can be changed by making healthy lifestyle choices, including:
- eating a healthy diet that’s low in processed foods and sugar
- avoiding alcohol
- maintaining a healthy weight
- exercising daily
- not smoking
By choosing the healthiest lifestyle options possible, you can empower yourself and make sure your breast cancer risk is as low as possible.
To learn more about breast cancer risk factors, visit the Breastcancer.org Lower Your Risk section.
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