Genetic link between skin cancer and moles found

New genetic evidence indicates that people with a greater number of moles have an increased risk of developing melanoma, the rarest but most dangerous of the three types of skin cancer. Having a large number of moles is well known to be a prominent skin-cancer risk-factor, but this is the first time a genetic basis for the link has been discovered. A consortium of European and Australian scientists compared some 300,000 genetic variants or'snips' (or SNPs, single nucleotide polymorphisms) in over 10,000 people and identified variations in two particular genes. People with both gene variants were found to have an increased risk of developing moles and almost double the risk of developing melanoma. The findings were published in the journal Nature Genetics.

Patients previously diagnosed with melanoma have been found to be far more likely to carry the gene variants closely linked to red-hair and freckles, and it is well known that those with fair skin who tend to sunburn easily are at most risk of developing melanoma. ‘This is what we expected to find', said Professor Tim Bishop of the University of Leeds, who led the study. ‘But the links seemed to be much stronger than we anticipated'. He added: ‘We had known for some time that people with many moles are at increased risk of melanoma. In this study we found a clear link between some genes on chromosomes 9 and 22 and increased risk of melanoma. These genes were not associated with skin colour'.

Instead, researchers from Kings College London found that variations in these genes were significantly associated with higher mole counts after they looked for common changes in 1,524 healthy adult female twins from the new TwinsUK registry. These initial results were then replicated in independent samples of adolescent twins from Brisbane.

Dr Mario Falchi, now at the Section of Genomic Medicine, Imperial College London, said: ‘Approximately one in eleven people of European ancestry carry two copies of both gene variants. These people show twice the number of nevi (moles) and double the risk for melanoma'.' Most people carry at least one of the two key variants, but the research shows that there are at least five genes which influence the risk of melanoma and someone who carries all five variants associated with an increased risk are around eight times more likely to develop melanoma than those carrying none.

The researchers hope that the new findings will eventually lead to the development of new treatments and better screening for the disease. However, the process by which genetics and sunlight combine to cause cancer in some people is still poorly understood at present. Professor Bishop explained: ‘If you take the people who have the greatest exposure to sunlight — those who work outside for example — and compare them to those with the least exposure, their risks of getting skin cancer are actually quite similar. Statistically, the differences are quite negligible. What we do know is that the combination of particular genes and a lifestyle of significant sun exposure is putting people at greatest risk'.