My friend was diagnosed with a melanoma on the bottom of her foot. I thought melanoma was caused by exposure to sunlight so how is this possible?"

Melanoma is a type of cancer which usually occurs on skin that has been overexposed to the sun. However, melanomas can also occur on parts of the body that have never been exposed to the sun. Like all cancers, melanomas are the result of changed or damaged genes that lead to cancer cells being able to grow and invade other tissues. UV rays can cause these genetic changes, but so can other factors. 

Around 10 per cent of melanomas occur in people with a family history. In these people, the odds that a melanoma will appear on a hidden body part are higher than for others because of the genes they’ve inherited. However, melanomas can also occur in people, even where there isn’t any obvious family history. It is possible a small proportion of melanomas unrelated to sun might also arise because of factors like viruses, chemicals and environmental pollutants. More research is needed to confirm this. Regardless of the time you spend in the sun or your family history, it’s important to get to know your skin – all of it, not just the parts exposed to the sun – and report any changes to your GP.