Moles on the skin increase skin cancer risk

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Published: 11 Sep 2014
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Dr Eugene Ong - University of Oxford, Oxford, UK

Dr Ong talks to ecancertv at the XV World Congress on Cancers of the Skin in Edinburgh, UK, about his work which found that moles on the skin can quadruple your risk of developing melanoma.

Read the article for more. 

The research that we’re doing is looking at the associations between having a hospital diagnosis of a mole and subsequently developing malignant melanoma, one of the most dangerous skin cancers. So we have data and access to the National Hospital Episode Statistics for the whole of England, so we have data for all the NHS hospitals in England from the year 1999. We constructed two groups, one of them was a mole group, so these people had visited hospital and been coded and diagnosed as having a mole in hospital or in a day case health visit. The other group was a group which didn’t have a diagnosis of mole. Comparing those two groups our overall finding was that people with moles were actually at significantly increased risk of developing melanoma within our study period. The overall risk, discounting the first year which potentially has confounding factors of misdiagnosis within the first year, so discounting that first year the increased risk, the people in the mole group were at 4.7 times increased risk compared to the non-mole group of developing malignant melanoma.

The two other significant findings that broadly we had were that these increased risks persisted long after the initial diagnosis. So the increased risks were still significant 5 years down the line from the initial diagnosis of the mole and also occurred at different sites to the original mole. So, for instance, if you had an increased risk of having a mole… if you were diagnosed with having a mole in the face you also had increased risks of developing melanoma elsewhere in the body, like the legs, the torso and other areas as well.

When should we worry about our moles?

While we had large amounts of numbers, so our study was very highly powered, we didn’t have a lot of individual level detail on exactly how many moles or how atypical they were. One can assume if these patients are pitching up to hospital and self-presenting and requiring hospital diagnosis of a mole then these are likely to represent a more atypical end of the spectrum, so moles that are perhaps funny looking or more numerous. That’s why the risks that we find are greater, perhaps, than in other studies.

How many patients were in your study?

We consulted these two cohorts and the mole cohort we looked at over 270,000 people with hospital diagnoses of moles and we compared that with our control hospital cohort which had over ten million patients.

What do you think will be the impact of these findings?

Several things, I think. Firstly it fully demonstrates the increased risk, particularly in this particular hospital cohort of developing the malignant melanoma, which is something they should be extra vigilant and, obviously, the usual sun protection and sun awareness advice would apply especially to these groups of patients. Secondly, the finding of being diagnosed with a mole that is benign was perhaps previously thought to be an all clear for these patients but what our studies suggest are that even if you have been diagnosed with a benign mole that you are at increased risk still of having malignant melanoma in the future, both at that site and at other sites as well.

So it’s important to remain vigilant, even if given the all-clear?

What we found in our study is not… the knowledge that having a large number of moles, or a large number of atypical moles, it’s well known that they’re both independent risk factors for developing melanoma. So that’s not an entirely novel finding but our study looked at a very large number of these hospital cohort so the finding of particularly the increased risk in this group is perhaps something that we should look at being extra vigilant.