SWOG S0000: SELENIUM AND VITAMIN E CANCER PREVENTION TRIAL (SELECT)

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Prostate cancer has been the most common malignant tumor (excluding non-melanoma skin cancer) in U.S. men for the last decade. It has been estimated that the lifetime risk of developing prostate cancer is 16.6% for Caucasian males and 18.1% for African-American males, and the overall prostate cancer mortality risk for men age 50 is 2.9% (Ries, et. al. 1998, Scher; et. al. 1995). An ideal method to reduce the mortality and morbidity of carcinoma of the prostate would be through primary prevention: either through a reduction in the number of life-threatening, clinically-evident cases or through a reduced age-dependent rate of development of the disease, i.e., the disease would become evident 5, 10, 15 years later than otherwise would occur. Although there is evidence that the development of this tumor may be related to dietary habits, problems in changing such patterns of behavior and the need for life-long intervention make such a preventative method difficult in practice (Mishina, et. al., 1985). The purpose of this study is to compare the effects of the study supplements. The supplements are selenium (L-selenomethionine), vitamin E (alpha-tocopherol), selenium plus vitamin E and placebo (a pill containing no active substances). We want to see whether the supplements, other than the placebo, can prevent or reduce the occurrance of prostate cancer. In both selenium and vitamin E, the strongest evidence for their potential roles in preventing prostate cancer comes from secondary findings of two randomized, placebo-controlled clinical trials. The development of these two supplements has arrived at the stage where a randomized, placebo-controlled intervention is needed to test the primary hypothesis regarding these supplements' prostate cancer chemoprevention effects (Taylor, Albanes, 1998). Data indicate that activities of selenium and vitamin E are complementary and that the two supplements act synergistically to inhibit carcinogenesis (Hoekstra, 1975; Medina, 1986; Thompson, 1994). This evidence makes the 2x2 factorial design for simultaneously testing both supplements a particularly attractive option for the confirmatory Phase III trial. No studies looking at the effect of using both selenium and vitamin E have been done. Based on past studies using other agents as well as the two supplements we are testing here, we believe that men may get an added benefit from using these two supplements together. The main purpose of this trial is to learn more about prostate cancers in healthy men that are found as part of regular medical care. We want to know whether the study supplements can prevent or decrease these cancers.