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| |  Selenium May Worsen Prostate Cancer in Men With SOD2 Gene Variant BOSTON -- June 25, 2009 -- Higher selenium levels in the blood may worsen prostate cancer in some men who already have the disease, according to a study published early online and appearing in an upcoming print issue of the Journal of Clinical Oncology. A higher risk of more-aggressive prostate cancer was seen in men with a certain genetic variant found in about 75% of the prostate cancer patients in the study. In those patients, having a high level of selenium in the blood was associated with a 2-fold greater risk of poorer outcomes than men with the lowest amounts of selenium. By contrast, the 25% of men with a different variant of the same gene and who had high selenium levels were at 40% lower risk of aggressive disease. The variants are slightly different forms of a gene that instructs cells to make manganese superoxide dismutase (SOD2). The research findings suggest that “if you already have prostate cancer, it may be a bad thing to take selenium,” said senior author Philip Kantoff, MD, Lank Center for Genitourinary Oncology, Dana-Farber Cancer Institute, and Harvard Medical School, Boston, Massachusetts. The unexpected results are the first to raise concern about this potentially harmful consequence of taking supplemental selenium. :These findings are interesting particularly in light of the recent negative results from the SELECT prevention study, which asked if selenium could protect against prostate cancer,” said Dr. Kantoff. Previous studies had found that the risk of developing prostate cancer was modified by a strong interaction between SOD2 and selenium. The new research was designed to look at the effect of this interaction on men already diagnosed with prostate cancer. The researchers examined banked blood samples, DNA, and medical records of 489 male Dana-Farber patients diagnosed between 1994 and 2001 with localised or locally advanced prostate cancer. Their mean age was 62, and their mean prostate-specific antigen (PSA) measurement was 6.0 ng/mL. About half the men were assessed as having a good disease risk, one-third had an intermediate risk, and the remaining one-sixth were at poor risk. Researchers measured the level of selenium in the blood and, using the stored DNA, they determined the SOD2 genotype -- the specific form of the SOD2 gene carried by each patient. Simply having a high level of selenium was associated with a slightly elevated risk of aggressive prostate cancer. But the risk was much more strongly affected by the interaction of selenium levels and whether the patient had a certain variant of the SOD2 gene. Men with the highest selenium levels and the AA form of the SOD2 gene were 40% less likely to have been diagnosed with aggressive prostate cancer than the men with same gene form but low levels of selenium. But for men carrying the V form of the gene, selenium had the opposite effect. In these men, those with the highest levels of selenium in their blood were about twice as likely to have an aggressive type of prostate cancer as their counterparts with low selenium levels, said Kantoff. The study couldn’t determine whether any of the men had been taking selenium supplements or not. “Among the 25% of men with the AA genotype, having greater selenium levels may protect against aggressive disease,” the authors concluded. “However, for the 75% of men who carry a V allele, higher selenium levels might increase the likelihood of having worse characteristics.” Therefore, they add, it is important to know which type of SOD2 gene a man has when considering the risks and potential benefits of taking selenium supplements. SOURCE: Dana-Farber Cancer Institute
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