Selenium, vitamin E, and the SELECT trial

The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was the largest prostate cancer prevention trial designed to date. It started enrolling patients in August of 2001 and closed to enrollment in June 2004 with a total of over 35,000 participants, of whom about 15 percent were African Americans.

In late October 2008, an initial review of study data by an independent trial monitoring group indicated that:

  • There was no potential for clinical benefit in continuing the trial.
  • There were suggestions that continuing treatment with selenium might be associated with an increased risk for type II diabetes
  • There were suggestions that continuing treatment with vitamin E might be associated with a slight increase in risk for prostate cancer.

Considering the size of this trial, it was a relatively simple, randomized, double-blind, multi-center study. Patients were randomized to one of four arms, as follows:

  • Arm I: Participants receive two different oral placebos once daily.
  • Arm II: Participants receive oral selenium and oral placebo once daily.
  • Arm III: Participants receive oral vitamin E and oral placebo once daily.
  • Arm IV: Participants receive oral selenium and oral vitamin E once daily.

Treatment of patients was originally projected to continue for 7-12 years. Results of the trial were not expected before about 2015.

SELECT had multiple outcomes measures and objectives, but the three most important and primary questions asked were:

  • Does selenium alone lower the clinical occurrence of prostate cancer compared to placebo and/or vitamin E?
  • Does vitamin E alone lower the clinical occurrence of prostate cancer compared to placebo and/or selenium?
  • Does the combination of vitamin E and selenium lower the clinical occurrence of prostate cancer compared to placebo, selenium, or vitamin E alone?

Previous studies had suggested that selenium and vitamin E (alone or in combination) might have some impact on men’s risk for developing prostate cancer, but only a trial of the size of SELECT was going to be able to confirm (or, as it turns out, deny) these initial findings.

Additional information about SELECT can be obtained on a web site organized by the Southwest Oncology Group (the coordinating organization for SELECT). Information is also available on ClinicalTrials.gov and on the web site of the National Cancer Institute.

Content of this page last reviewed and updated March 26, 2011.
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