Selenium May Increase Nonmelanoma Skin Cancer Risk

BUFFALO, N.Y.--Selenium supplementation does not appear to prevent nonmelanoma carcinomas and may slightly increase the risk of a certain type of nonmelanoma carcinoma, according to a clinical trial published in the Oct. 1 issue of the Journal of the National Cancer Institute (95, 19:1477-81, 2003) (jncicancerspectrum.oupjournals.org).

Carcinomas--cancers that begin in the cells that cover or line an organ--can originate in basal and squamous cells, which are the two cellular layers of the epidermis. Basal cell and squamous cell carcinomas--both considered nonmelanoma skin cancers--are the two most common forms of skin cancer, according to the National Cancer Institute (NCI). NCI added that basal cell carcinoma accounts for more than 90 percent of all skin cancers in the United States and is a slow-growing cancer that does not have a tendency to metastasize. Similarly, squamous cell carcinoma does not spread very often, but it does so more often than basal cell carcinoma.

To study the effects of selenium supplementation on preventing nonmelanoma skin cancers, James R. Marshall, Ph.D., of the Buffalo, N.Y.-based Roswell Park Cancer Institute, and colleagues from across the United States evaluated data from the Nutritional Prevention of Cancer Trial, a double blind, placebo-controlled clinical trial designed to test whether 200 mcg/d of selenium (as selenized yeast) would prevent nonmelanoma skin cancer among 1,312 patients who previously had the disease. Researchers did not find a significant association between selenium supplementation and the risk of basal cell carcinoma, although the mineral was associated with a statistically significant increase in the risk of squamous cell carcinoma and total nonmelanoma skin cancer. "I am not sure what is going on with this agent in the skin," Marshall told INSIDER. "Clearly, it does not appear to offer protection against skin cancer. Whether it actually increases risk is not as clear. ... Our best estimate is that selenium does not increase risk by much."

In their study, researchers concluded results from the Nutritional Prevention of Cancer Trial showed those at high risk of nonmelanoma skin cancer did not benefit from selenium supplements. Marshall added these results could have been due to the possibility of a reaction between selenium and arsenic. Another interesting potential was that the study subjects already had skin damage. Marshall stated, "As we noted in the report, most of these people had highly initiated skin that had endured lots of sun damage. It is possible the damage was irreparable."

Because squamous cell carcinoma is non-fatal, the risks associated with selenium consumption are minor compared to the benefit selenium can provide in preventing prostate cancer, according to Suzanne Stratton, Ph.D., associate research assistant at Tucson, Ariz.-based Arizona Cancer Center and another investigator on the trial. "My concern when this came out is that the media gets emotional about things because it makes it more interesting," she said. "I don't think it'll hurt the industry. I think it makes it even more important that we study this agent in human beings, as long as people are aware of the risks and the potential for tremendous benefit."