Simple Melanoma Risk Test: Count the Moles on an Arm

Liam Davenport

October 21, 2015

An individual's risk for melanoma can be quickly and simply assessed in primary care by counting the number of nevi on one arm, suggests a group of Italian and United Kingdom researchers.

Using data derived from a study of more than 3500 female twins, they found that total body nevus count (TBNC) is significantly predicted by the number of nevi on the arm.

"It's important because the number of moles on the body is strictly related to the risk of melanoma, and if you have more than 100 moles on your body, the risk increases by some five to six times in the white population," lead researcher Simone Ribero, MD, PhD, Department of Twin Research and Genetic Epidemiology, King's College London, United Kingdom, told Medscape Medical News.

The researchers demonstrated that a nevus arm count of more than 11 is associated with a significant risk of having more than 100 nevi.

The arm was also the most predictive site for total body nevus counts when the study was replicated in a control population that included both sexes, say Dr Ribero and colleagues.

The team therefore recommends that "this fast clinical evaluation should be used for a quick estimation of melanoma risk in general practices."

The tool is limited but useful, suggested Dr Ribero.

"The risk of developing melanoma is not only in the arm, so we can't just look at one arm of the patient and predict perfectly the risk of melanoma, but this could be a tool to understand the general number of moles, and in this way we have a very quick way of understanding the risk of developing melanoma," he said.

The research was published online October 19 in the British Journal of Dermatology.

Progress has been made in characterizing germline and somatic mutations in melanoma in recent years. However, TBNC remains the most important risk factor for the development of melanoma.

Counting the number of nevi on the body is both time-consuming and impractical for clinicans, the authors point out. Thus, a number of studies have used selected body sites as proxies for TBNC to estimate melanoma risk.

For the current investigation, the team studied data on 3694 female twins (median age, 47 years) who took part in the TwinsUK study between January 1995 and December 2003 and for whom skin examination and baseline data were available.

Skin examinations included skin type, hair and eye color, and freckles, along with the nevus count on 17 body sites. The examinations were carried out by trained nurses.

The overall mean nevus body count was 32. This declined steadily after age 30 years (P < .001), corresponding to a decrease of 4 nevi per decade of life between ages 30 and 60 years.

The body areas that were most predictive of TBNC were the arms and legs, with adjusted correlation coefficients of 0.50 and 0.51 for the right and left arms, respectively (P < .001) and 0.49 and 0.48 for right and left legs, respectively (P < .001).

Thus, the nevus count on the legs was also predictive of TBNC, but the authors favored the arm, which yielded the highest correlations and, for clinical practice, is a more accessible site.

To confirm the findings, the team analyzed data on the control group from a melanoma case–control study conducted in the United Kingdom that used the same protocol.

The study involved 162 men and 253 women (mean age, 45 years), for whom the average TBNC was 33 and 35, respectively.

Adjusting for age, height, skin type, and sex, statistical analysis revealed that the most predictive body site for TBNC was the right arm in both men and women (for the whole arm, adjusted r = 0.86; P < .001; for the arm above the elbow, adjusted r = 0.83; P < .001).

The area under the receiver operating characteristics curve (AUC) was then calculated using data from the TwinsUK cohorts and female data from the replication cohort to determine the best cutoff point for predicting TBNCs of 50 and 100.

This indicated that a nevi count of seven on the right arm best predicted women having a TBNC of more than 50 (AUC, 0.74; adjusted odds ratio, 8.81). For a TBNC of more than 100, a nevi count on the right arm of 11 was the best predictor in women (AUC, 0.71; adjusted odds ratio, 9.38).

Discussing the results, Dr Ribero commented: "We know that having more than 10 moles is a high risk and having two moles is a low risk, so each mole that we increase on the arm means that we have more on the body.

"We know that to have more than 100 [on the body] increases by five to six times the risk," he said.

Noting that although there are other risk factors associated with melanoma, TBNC is the strongest, Dr Ribero said: "People that are very moley know that they are at risk of melanoma, of course, but no one knows what is the limit of what is 'moley' or 'not moley,' so we just want to help general physicians and practitioners [in deciding] when to screen for melanoma."

The new research is not novel and reinforces earlier work.

In a previous Australian case-control study, the right arm was considered a strong predictor of melanoma risk, with various cutoffs of nevus counts at that site; for example, more than 10 nevi on the whole arm increased the risk for melanoma 11-fold (J Natl Cancer Inst. 1984;72:257-66).

The study received no funding. The authors have disclosed no relevant financial relationships.

Brit J Dermatol. Published online October 19, 2015. Abstract


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