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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
The Selenium and Vitamin E Cancer Prevention Trial (SELECT) Klein, Thompson, Tangen, et al. J Amer Med Assoc, Oct 12, 2011; Vol 306, No.14; 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 Anticoag, hemorrhagic stroke, blood pressure are due to Vitamin E’s anti-coagulative properties.

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 Not mandatory, as the benefits of these screens were under debate and were expected to change during the trial.

7 Methods Study was blinded until 10/23/2008, when participants discontinued use of study agents Non-blinded follow-up occurred until 07/2011 Study facilitators met in 2008 and determined that, according to the data, agents were not effective in reducing prostate cancer, and could not be before the end of the study. Results were published in 2008.

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 1to compare prostate and other cancer incidence between placebo and each of the 3 study groups with active agents

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 Vitamin E + Selenium (n=8702)
Results Placebo (n=8696) Vitamin E (n=8737) Selenium (n=8752) Vitamin E + Selenium (n=8702) No. of prostate cancers 529 620 575 555 Hazard ratio (99% CI) 1.17 ( ) 1.09 ( ) 1.05 ( ) P value 0.008 0.18 0.46 Absolute Risk 9.3 10.9 10.1 9.7 Gleason >7, No. 133 155 161 164 Hazard Ratio (99% CI) 1.16 ( ) 1.21 ( ) 1.23 ( ) 0.20 0.11 0.08 hazard ratio= time factor that study arm will reach outcome measure

12 Vitamin E + Selenium (n=8702)
Results Placebo (n=8696) Vitamin E (n=8737) Selenium (n=8752) Vitamin E + Selenium (n=8702) All cancers 1108 1190 1132 1149 Hazard ratio (99% CI) 1.07 ( ) 1.02 ( P value 0.13 0.59 0.60 Diabetes 869 918 913 875 Relative risk (99% CI) 1.05 ( ) 1.04 ( ) 0.99 ( ) 0.29 0.34 0.91 No secondary endpoint - colorectal cancer, lung cancer, death, CVE, all cancer, or diabetes - had significant results. The 2009 results of the SELECT trial had a diabetes incidence with selenium HR of 1.07

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 ATBC - smoker one, PHS II - 400IU QOD had no effect on prostate cancer incidence naturally occurring dietary constituents are part of normal physiology and a U-shaped-dose response curve may exist where deficiency or supraphysiological doses are harmful.

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 =

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

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; National Cancer Institute. “A Snapshot of Prostate Cancer.” Sep < National Institutes of Health. “Dietary Supplement Fact Sheet: Vitamin E.” Oct < Heinonen et al. Prostate cancer and supplementation with alpha-tocopherol and beta-carotene: incidence and mortality in a controlled trial. J Natl Cancer Inst Mar 18;90(6):440-6.

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