Selenium Increases Risk of One Type of Skin Cancer

Healthnotes Newswire (December 18, 2003)—Individuals with a history of certain types of skin cancer are more likely to have a recurrence of one particular form of skin cancer if they take selenium supplements, according to a report in the Journal of the National Cancer Institute (2003; 95:1477–81). While this finding is of concern, the bulk of the evidence still supports the conclusion that selenium is an important anti-cancer nutrient.

Three different types of skin cancer occur commonly in humans: melanoma, which is the most serious, can spread throughout the body (metastasize) and is often fatal; two other skin cancers, basal cell carcinoma and squamous cell carcinoma, are considered less serious and generally have a good prognosis, unless they are neglected for too long.

The new study is a follow-up report on a clinical trial that began 20 years ago. In that trial, 1,312 people with a history of non-melanoma skin cancer (i.e., basal or squamous cell carcinoma) were randomly assigned to receive 200 mcg of selenium per day (in the form of high-selenium yeast) or a placebo for 4.5 years. Compared with the placebo group, the selenium-treated group had a 25% increase in the risk of developing a new squamous cell carcinoma. The incidence of basal cell cancer did not differ between the selenium and placebo groups.

Despite this finding, the overall benefits of selenium in this study still appeared to outweigh the risks by a significant amount. As pointed out in an earlier report (Journal of the American Medical Association 1996;276:1957–63), the total number of cancer deaths was 50% lower in the selenium group than in the placebo group. In addition, the total number of cancers (excluding skin cancers) was reduced by 37%; the incidence of lung cancer was reduced by 46%, colorectal cancer by 58%, and prostate cancer by 63%.

Thus, the increased risk of a usually non-fatal skin cancer was more than counterbalanced by a reduction both in cancer-related deaths and in the incidence of other forms of cancer. For that reason, supplementing with selenium still appears to be a reasonable strategy for people interested in preventing cancer. Those with a history of squamous cell carcinoma should be examined frequently for signs of new lesions, especially if they are taking selenium supplements. Some 95 to 98% of squamous cell carcinomas can be cured if they are treated early and have not spread. In addition, because excessive sun exposure is the major cause of squamous cell carcinoma, people at risk of developing the disease should not stay out in the sun too long.