By Mo McNulty
How can you tell if you’re at risk for developing a deadly skin cancer? According to a new study, it may be as simple as counting the number of moles on your right arm.
Why do we need to keep track of numbers of moles?
Moles are groupings of skin cells that are often black or brown and usually appear raised from the rest of the skin. They are linked to melanoma, a deadly skin cancer. According to the American Cancer Society, nearly 74,000 new cases of melanoma will be diagnosed in 2015, and nearly 10,000 will die from the disease.
So, how exactly do moles relate to melanoma? Melanoma only rarely develops at the site of a mole – more often, it develops at a new spot on the skin. However, many studies have found an association between the number of moles on the body and the risk of developing melanoma. The Skin Cancer Foundation reports that anyone with more than 100 moles has a higher risk, while the Melanoma Education Foundation says that your risk rises if you have at least 50 moles. Either way, doctors have long recommended keeping track of your overall number of moles, as well as their appearance – if a mole changes in shape, size, or color, it may be an early warning sign of cancer.
Why did researchers conduct this study?
It may be difficult for many people, especially those with a large number of moles and freckles, to count all of the moles on their body. Therefore, researchers are interested in coming up with a measure to estimate the total number – can you count the number of moles in one location on your body, and use that number to estimate the total? The answer seems to be yes: past studies have found a link between the number of moles on certain body areas with the overall total mole count.
Several characteristics distinguish this most recent study from these past studies. Ribero and colleagues used a cohort of volunteers that was larger than previous studies, consisting of 3694 women. An additional key difference was that study participants were not recruited specifically for a skin cancer study – many past studies have recruited people when they came in to the dermatologist’s office to be screened for melanoma. Because the women in this study were already a part of a larger cohort which aimed to study a number of different health measures, the authors eliminated possible bias by not selecting women already worried about melanoma. This means that this study may be more generalizable to the whole population.
How did the study authors end up focusing on moles on the right arm?
The researchers measured the number of moles on 17 different body sites for each woman. The table below shows the mean number of moles found on each body site, the standard deviation, and the Spearman’s correlation coefficients, which measured the association between moles at that body site and total number of moles on the body. The higher the correlation coefficient, which here is adjusted for age, height, and skin type, the closer the link between number of moles at a site and total number of moles.
Both arms and legs were the sites with the highest amount of correlation. Ribero and colleagues repeated this study in a different group of people that consisted of both men and women, and found that in this cohort, the right arm had the highest correlation coefficient. They concluded that this body site was the most predictive of total number of moles. Specifically, people with at least 11 moles on their right arm are likely to have at least 100 moles on their whole body.
Why is this study important?
Counting the number of moles on one arm is much easier than counting all of the moles on the body. This could be a quick and easy way for doctors to estimate a patient’s melanoma risk. However, it is important to note that this study did not actually look at whether each patient developed melanoma. While it is likely that there is a link between number of moles on the arm and melanoma risk, since both are associated with high numbers of moles on the body, it is possible that this link is not that strong. This may be a good direction for future studies.
Ribero S, Zugna D, Osella-Abate S, Glass D, Nathan P, Spector T, Bataille V. Prediction of high naevus count in a healthy UK population to estimate melanoma risk. Br J Dermatol 173, 3 (2015). PMID: 26479165
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