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Vitamin E and the Risk of Prostate Cancer

Vitamin E and the Risk of Prostate Cancer. Klein, Thompson, Tangen, et al. J Amer Med Assoc, Oct 12, 2011; Vol 306, No.14; 1549 - 1556. The Selenium and Vitamin E Cancer Prevention Trial (SELECT). Zachary Lapaquette PharmD Candidate University of Georgia. Background.

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Vitamin E and the Risk of Prostate Cancer

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  1. Vitamin E and the Risk of Prostate Cancer Klein, Thompson, Tangen, et al. J Amer Med Assoc, Oct 12, 2011; Vol 306, No.14; 1549 - 1556 • The Selenium and Vitamin E Cancer Prevention Trial (SELECT) Zachary Lapaquette PharmD Candidate University of Georgia

  2. Background • 16% of men will be diagnosed with prostate cancer in their lifetime1 • Most common type of cancer in U.S. men, other than non-melanoma skin cancer2 • Second leading cause of cancer-related death in U.S. men

  3. Background • Vitamin E is fat-soluble and has anti-oxidative properties • Recommended daily allowance for vitamin E is 22.4IU (15mg) daily3 • Doses of 50IU/day were shown to decrease prostate cancer incidence in smokers4

  4. SELECT Trial • Randomized, placebo-controlled, multi-center trial • Compared selenium 200mcg/day, vitamin E 400IU/day, or both against placebo • Planned follow-up minimum of 7 years and maximum of 12 years

  5. Inclusion Criteria • Healthy • Age 50 or older for African Americans, or 55 for all other men • No h/o prostate cancer diagnosis • PSA < 4ng/mL • Normal DRE • No current use of anticoagulants • No h/o hemorrhagic stroke • Normal blood pressure

  6. Methods • Participants without prostate cancer had clinic visits every 6 months; with prostate cancer, annually • Annual PSA and DRE were not mandatory • Prostate cancer status was determined by self-report at each 6-month visit • Pathology report, tissue then sent to SELECT

  7. Methods • Study was blinded until 10/23/2008, when participants discontinued use of study agents • Non-blinded follow-up occurred until 07/2011

  8. Statistical Analysis • Primary end point: Prostate cancer incidence as determined by routine clinical management • Other areas of study: colorectal cancer, lung cancer, all other primary cancers, deaths (all cause), development of diabetes, CVE • 1- and 2-sided P values given

  9. Statistical Analysis • Proportional hazards model used • Unlike linear regression, proportional hazards models do not assume normal distribution and allow for censored data • Men without end-point of interest were censored at last contact date • Chi-squared test used to test the difference in the relative risk of diabetes

  10. Results • Total of 35,533 men randomized at 427 centers into placebo (n=7594 had final follow-up data), vitamin E (n=7650), selenium (n=7626), selenium +vitamin E (n=7620) • No significant differences in age, race, baseline PSA, or diagnostic testing

  11. Results

  12. Results

  13. Authors’ Comment • An explanation for the increased risk of prostate cancer in the vitamin E arm is not apparent • The insignificant increased risk in the vitamin E + selenium arm implies that selenium may have a protective effect • This study is seems to contradict ATBC and PHS II studies • Caution should be used when recommending or studying high doses of micronutrients • Health effects from these agents may continue even after the intervention is stopped

  14. Conclusion • Healthy men with average risk of prostate cancer subjected to contemporary community standards of screening and biopsy who took a common dose of vitamin E have a significantly increased risk of prostate cancer. • The increased risk implies that seemingly innocuous yet biologically active substances such as vitamins can cause harm • Consumers need be skeptical of health claims for unregulated over-the-counter products in the absence of strong evidence of benefit

  15. Presenter’s Comment • Study has good reach, but is limited to healthy men 50+ years old • Criticism of study: • Did not have best- and worst-case censure analysis • Data collection dependent on self-report • 427 research sites • Overall strong study • Placebo event rate: 529/8696 = 0.0608

  16. Presenter’s Comment • NNH = 98 • Vit E prostate cancer rate: 620/8737 = 0.0710 • Placebo prostate cancer rate: 529/8696 = 0.0608

  17. Works Cited • Klein, Thompson, Tangen, et al. Vitamin E and the Risk of Prostate Cancer: The Selenium and Vitamin E Cancer Prevention Trial. J Amer Med Assoc, Oct 12, 2011; Vol 306, No.14; 1549 - 1556 • National Cancer Institute. “A Snapshot of Prostate Cancer.” Sep 2010 <http://www.cancer.gov/aboutnci/servingpeople/snapshots/prostate.pdf> • National Institutes of Health. “Dietary Supplement Fact Sheet: Vitamin E.” Oct 2011 <http://ods.od.nih.gov/factsheets/VITAMINE> • Heinonen et al. Prostate cancer and supplementation with alpha-tocopherol and beta-carotene: incidence and mortality in a controlled trial. J Natl Cancer Inst. 1998 Mar 18;90(6):440-6.

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