Wolf, I don’t think they have even got that far (working out what causes it) I mean they know in general terms that cells which are irritated tend to mutate and also that as we get older, we are more likely to produce mutated cells but why some people are more likely to have cells which mutate than other people (apart from heredity, and even then its an observed fact rather than knowing why) The other thing I remember being told by an oncologist years ago is that cell mutation is a natural part of life. Its a part of the mechanism of evolution. He also said that if you looked for it (he did in the sixties as part of his research) a huge percentage of people over 70 who died of something else entirely and had never had cancer diagnosed, would have a cancerous mass somewhere within their body, so not a skin cancer. It would probably be small and non metastatic but it would be there. My husband’s oncologist said something similar. He said that nowadays when people are diagnosed with cancer, if there is the possibility that it has spread, they are scanned and checked over in ways that were not possible in the recent past. The scans and imaging show up things which would not previously have been found and its sometimes not easy to know what to do about them because its not clear what the risk is.