Skin cancer and sun exposure

There are three main forms of skin cancer. The rarely fatal but common basal cell carcinoma and squamous cell carcinoma and the rare but commonly fatal malignant melanoma.

Basal cell carcinoma and squamous cell carcinoma usually appear on areas of the body exposed to UV light (from the sun or other sources). They are usually treated surgically. Sun exposure is definitely a risk factor for these two forms of skin cancer. In contrast, the picture is not at all clear cut when it comes to the third type of skin cancer, melanoma. This condition represents a mere 3% of all skin cancers but leads to three quarters of skin cancer deaths.

Science-based medicine recently reported that there is no good evidence to demonstrate that reducing sun exposure has an effect on melanoma risk. Indeed, the site points out something about which I wrote for New Scientist back in 1990 that chronic (i.e. long-term) sun exposure actually seems to have a protective effect. Moreover, there is now reasonable evidence that safe sun exposure reduces the risk of other types of cancer, although the jury is, inevitably still out with its hat and suncream on regarding that notion). Cancer charities dispute the claims that any form of tanning is ever safe.

It seems that a genetic predisposition to melanoma is a major factor in its emergence. However, before we get complacent, there is strong evidence that links sun burn and intermittent sun exposure to melanoma. Similarly, tanning lamps may also show a dose-response relationship, says SBM: “Overall, the data points to an association between intentional sun exposure and melanoma, non-intentional sun exposure with squamous cell carcinoma, and basal cell carcinoma likely related to both.”

A new therapy for metastatic malignant melanoma is currently in trials and showing very promising results. The drug, now known as RO5185426 (previously PLX4032 and RG7204) is an inhibitor of the protein expressed by the B-RAF cancer-causing genetic mutation. This gene was found by spin-off research as part of the human genome project and represents one of the best known examples of the gradually emerging area of pharmacogenomics. About 80 patients have been in trials so far, and between 70 and 80% of them have seen tumour regression, often by about 50%, within weeks of entering the trial.

Until pharmacogenomics offered the possibility of targeted medicine based on a patient’s genetics, there was little point in developing specific drugs of this sort. However, there is a great deal of effort going into targeting the proteins made by specific mutations in this and other conditions.