Having few moles on the arm does not immunize against melanoma…

Having few moles on the arm does not immunize against melanoma…

Since the beginning of the week, many sites and newspapers have relayed under misleading titles a British study evoking a link between “number of moles on the arm” and “risk of melanoma”. A quick clarification is in order.

The articles follow one another, and the titles are similar: “Eleven moles on the right arm? You risk a melanoma”, “11 moles on the right arm: and if it was the sign of a melanoma?”…

The study which the newspapers thus echoed did not ask this question, nor did it come to this kind of conclusion. The objective of the researchers was, in fact, to find a fast method for estimate the total number of moles on an individual’s body. A count was made on 17 different areas of the body of 3,694 women with white skin. The researchers’ analysis shows that the number of moles on the right forearm is proportional to that present on the whole body[1].

Why count moles (or nevus)? And what is the link with melanoma?

First, about 30% of melanomas derive from pre-existing moles (most frequently, since an atypical mole[2]) Each year, approximately one in 34,000 French people sees one of her moles turn into melanoma[3]. If we consider that each mole is a potential emergence site, the likelihood of developing melanoma logically increases with their number.

However, epidemiology shows that this probability increases faster Again. A major meta-analysis published in 2005 shows that people between 16 and 40 moles on the whole body have an increased risk of around 50% of develop melanomacompared to those who have less than 16. But this relative risk is around 600% in people with between 101 and 120 moles on the body![4]

Notably, the melanomas in question here do not all derive from a nevus. One of the explanatory hypotheses is that the phenomena governing the appearance of moles (these generally appear during childhood, the process being able to continue in adulthood, until about 40 years of age) have common roots with those promoting the emergence of melanomas.

Clinicians have therefore long known that people with many moles all over the body require special monitoring. Counting all nevi being tedious, the – intuitive – trick of estimating the total number by looking at a small part of the body has been suggested in studies for at least twenty years. The work published this week confirms that the arm, and even the forearm, are representative sites of the entire surface of the skin.

Ambiguous, even misleading titles

We understand, contrary to what multiple media headlines, to have eleven moles on the right arm is nota sign of melanoma. Have eleven moles on right arm is also notthe threshold from which an individual becomes “at risk” of developing this type of cancer.

So do not run to your dermatologist if you count eleven spots on your arm. Above all, do not think you are “immune” if your score is lower than that announced in the press.

Let us emphasize the fact that the examination of the arm only provides statistical information, useful for the identification of risk profiles. It absolutely cannot detect a melanoma that has appeared elsewhere on the body. Frequently it is up to the patient to identify any change in the size, shape, color or texture of a mole, over the entire surface of his skinand inform your doctor.

Let us add, to conclude, that the number of nevi is not the predominant factor in the risk of melanoma. Among the other parameters influencing the risk, the clarity of the skin, the eyes, the color of the hair (blond or red), the fact of having had in the past the skin burned by a sunburn, also strongly influence the risk of skin cancer.

Currently, the best way to prevent all types of skin cancer (melanoma, skin carcinoma) remains to avoid overexposure to the sun and the use of UV lamps. Sun protection with an index equal to or greater than 20 is highly recommended.

Source : Prediction of high nevus count in a healthy UK population to estimate melanoma risk. Ribero S, Zugna D, Osell-Abate S, et al. British Journal of Dermatology. 2015 Oct 19. doi:10.1111/bjd.14216

[1] In the group studied, people with seven nevi on the right arm had more than 50 nevi on the whole body. For eleven nevi, the total number exceeded 100.

[2] We differentiate the common nevus from the dysplastic (or atypical) nevus. The dysplastic nevus is generally larger than the common nevus (more than 5mm in diameter). It has irregular borders, and its shade can be a mixture of several colors (ranging from pink to dark brown).

[3] Melanoma affects slightly more than one in 10,000 French people each year.

[4] The order of magnitude remains the same whether or not the types of nevus are differentiated.

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