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The SELECT Prostate Cancer Prevention Trial

  • Updated: 10/12/2011

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SELECT (the Selenium and Vitamin E Cancer Prevention Trial) is the largest-ever prostate cancer prevention trial. Preclinical and epidemiological studies had suggested that selenium and vitamin E (alone or in combination) might reduce the risk of developing prostate cancer by 60 percent and 30 percent, respectively, but only a large clinical trial such as SELECT could confirm those initial findings.

Initial data from SELECT, reported in late 2008, showed that daily selenium and vitamin in E supplements, taken either alone or together for a median of 5.5 years, did not prevent prostate cancer. The data also showed two concerning trends: a small increase in the number of prostate cancer cases in men taking only vitamin E, and a small increase in the number of cases of diabetes in men taking only selenium. Neither of these findings proved an increased risk from the supplements, and they could have been due to chance. These initial results were published in the Journal of the American Medical Association on January 7, 2009 (see the abstract).

Updated data from SELECT, reported in 2011, show that, after an average of 7 years (5.5 years on supplements and 1.5 off supplements), there were 17 percent more cases of prostate cancer in men taking only vitamin E than in men taking only placebos.  Specifically, for every 1,000 men who took placebos there were 65 cases of prostate cancer over 7 years; for every 1,000 men who took vitamin E, there were 76 cases of prostate cancer.  This difference, an absolute increase of 11 cases per 1,000 men, was statistically significant and therefore is not likely due to chance.  These results were published in the Journal of the American Medical Association October 12, 2011 (see the paper).

Participants in SELECT stopped taking their study supplements in 2008 but continued to have their health monitored by study staff to help determine the long-term effects of having taken either supplement or placebo and  to complete a biorepository of blood samples that will be used in extensive molecular analyses of prostate cancer, other cancers, and other diseases of men's aging.  Study centers are now closed and long-term follow-up is ongoing through the SELECT Coordinating Center in Seattle.

SELECT began enrolling patients on August 22, 2001; enrollment closed on June 24, 2004, after 35,534 participants had been enrolled. About 15 percent of the participants are African-American. Men were eligible to join the study if they were age 55 or older or, in the case of African-American men, age 50 or older. (African American men could join at younger ages because prostate cancer strikes African-American men earlier and more often than white men.) There were more than 400 SELECT sites throughout the United States, Puerto Rico, and Canada.

SELECT was coordinated by SWOG (formerly the Southwest Oncology Group), a network of more than 4,000 researchers at more than 500 institutions, and sponsored by the National Cancer Institute (NCI).

SWOG maintains a web page with information about SELECT.  Men who participated in SELECT and have questions about the trial, can contact the SELECT Coordinating Center by phone at 1-877-798-5444 (Espanol 1-877-740-3331) or by email at

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