I was reading this morning about a study which assessed the relationship between skin cancer risk and risk of other cancers . There are three main forms of skin cancer; squamus cell carcinoma (SCC), basal cell carcinoma (BCC) and malignant melanoma. This study found that having SCC or BCC was associated with an increased risk of having another cancer of 57 and 9 per cent respectively. Individuals with these cancers were, according to reports, more than twice as likely to be diagnosed with malignant melanoma and had an increased risk of smoking related cancers.
I have seen one of the study authors, Professor Liam Murray, quoted as offering potential explanations for these associations, including ” a new skin cancer may be more likely to be detected in patients who are monitored following their first diagnosis of skin cancer.” This seems fair enough to me, as individuals who have had a diagnosis of skin cancer are likely to have their skin scrutinised more closely and more regularly than those without this diagnosis, and any other cancer is therefore more likely to be detected and diagnosed.
Another of Professor Murray’s explanations for his findings is that “The increase in smoking-related cancers may be because smoking predisposes to skin cancer as well as other cancers or because people who smoke may be more likely to have generally unhealthy lifestyles including excessive sun exposure.” This seems eminently sensible too.
Another finding of this research was that individuals with malignant melanoma were more than twice as likely to develop another cancer compared to the general population. Professor Murray offered this explanation Sun exposure is an important risk factor for all types of skin cancers so patients who have had one type of skin cancer may be more likely to develop other types as well. However, I’m not so sure: Previously on this site I have cited some evidence which casts doubt on the notion that sunlight causes malignant melanoma. You can read a relevant piece here, which cites specific studies that suggest that increased sunlight exposure may actually help reduce melanoma risk.
Now, if that were to be the case, then those with a history of melanoma might actually, overall, have experienced reduced sun exposure. Bearing in mind that sunlight exposure appears to reduce the risk of several forms of cancer (see here), then this might explain why those with a history of malignant melanoma are at such higher risk of other forms of cancer. I don’t know whether this is the case or not, but the theory is at least plausible, I think, on the basis of the current evidence.
Cantwell MM, et al. Second primary cancers in patients with skin cancer: a population-based study in Northern Ireland. Br J Cancer 2009;100(1):174-7.