Selenium and Vitamin E Cancer Prevention 

Trial (SELECT): Questions and Answers 

Key Points

• SELECT stands for the Selenium and Vitamin E Cancer Prevention Trial, a 

clinical trial to see if one or both of these dietary supplements prevent prostate 

cancer (see Question 1). 

• Selenium and vitamin E are antioxidants. Earlier studies suggested that these 

supplements might prevent prostate cancer (see Questions 3, 4, and 5). 

• In order to participate in SELECT, men had to meet certain eligibility 

requirements (see Questions 6, 7, and 8). 

• Men who participate in this study were randomly assigned to take two capsules a 

day—selenium and vitamin E, selenium and a placebo, vitamin E and a placebo, 

or two placebos (see Question 10). 

• Participants are asked to provide toenail and blood samples, respond to an annual 

questionnaire, and pick up capsules every 6 months (see Question 13). 

1. What is SELECT?

SELECT stands for the Selenium and Vitamin E Cancer Prevention Trial, a clinical trial 

to see if one or both of these dietary supplements prevent prostate cancer. The trial is 

funded by the National Cancer Institute (NCI) and is being coordinated by the Southwest 

Oncology Group (SWOG), an international network of research institutions that receives 

NCI funding. Enrollment began in 2001 and ended in 2004, 2 years ahead of the 

originally planned 5 years. The study will continue for 7 years after the last man 

enrolled, meaning that each man will participate for 7 years or more, depending on when 

he joined the study. More than 400 sites in the United States, Puerto Rico, and Canada 

are taking part in the study. Over 35,000 men are participating in SELECT. 

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2. What are a man’s chances of developing prostate cancer? 

Except for skin cancer, prostate cancer is the most common type of cancer in men in the 

United States. In 2005, there will be an estimated 232,090 new cases of prostate cancer 

and 30,350 deaths from this disease in the United States (1). 

Approximately 1 in 6 men in the United States (or 17.8 percent) will develop prostate 

cancer during his lifetime (1). All men are at risk, but those at highest risk fall into one 

or more of the following categories: age 55 or older; black; or have a father or brother 

with prostate cancer. 

3. What is selenium? Why study it for prostate cancer prevention? 

Our bodies need selenium, a nonmetallic trace element that we get from food—especially 

plant foods like rice and wheat, seafood, meat, and Brazil nuts. Selenium is an 

antioxidant that might help control cell damage that can lead to cancer. 

The Nutritional Prevention of Cancer Trial, published in 1996, included 1,312 men and 

women who had skin cancer. Men who took selenium to prevent nonmelanoma skin 

cancer received no benefit from selenium in preventing skin cancer. However, men who 

had taken selenium for 61⁄2 years had approximately 60 percent fewer new cases of 

prostate cancer than men who took the placebo (2). In 2002, study data showed that men 

who took selenium for more than 71⁄2 years had about 52 percent fewer new cases of 

prostate cancer than men who took the placebo (3). This study is one of the reasons 

selenium is being studied in SELECT. (See Question 11 for more information about 

selenium.) 

4. What is vitamin E? Why study it for prostate cancer prevention? 

We get vitamin E in a wide range of foods, especially vegetables, vegetable oils, nuts, 

and egg yolks. Vitamin E, like selenium, is an antioxidant, which might help control cell 

damage that can lead to cancer. 

In a 1998 study of 29,133 male smokers in Finland, men who took vitamin E to prevent 

lung cancer had 32 percent fewer new cases of prostate cancer than men who took the 

placebo. Some men also took beta carotene, but neither substance helped prevent lung 

cancer (4). (See Question 12 for more information about vitamin E.) 

5. What do researchers hope to learn from SELECT? 

SELECT is the first study to look directly at the effects of selenium and vitamin E on the 

risk of prostate cancer. This study is designed to find out if selenium, vitamin E, or both 

prevent prostate cancer. 

A large trial of selenium and vitamin E is needed to substantiate earlier, separate findings 

from studies in which prostate cancer was not the primary outcome. Although two earlier 
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studies suggested that these two supplements might prevent prostate cancer, this cancer 

was not the focus of those studies. The primary goal of SELECT is to assess the effect of 

these substances on the number of new cases of prostate cancer diagnosed during routine 

clinical practice. Other objectives are to assess the impact of selenium and vitamin E on 

the incidence of lung and colon cancer, as well as on survival. SELECT will study the 

molecular genetics of cancer risk and associations between diet and cancer. Additionally, 

SELECT will examine quality of life. 

6. Who was eligible to participate in SELECT? Were there restrictions on eligibility? 

Many diseases, including prostate cancer, occur more frequently in older persons. The 

risk of developing prostate cancer increases with age. More than 92 percent of prostate 

cancer cases occur in men age 55 and older. 

Black men had to be age 50 or older to participate, and men of other races and ethnicities 

had to be 55 or older. The age for eligibility was lower for black men because, on 

average, they get the disease at an earlier age. In addition, black men in the United States 

have the highest incidence of prostate cancer in the world. Thus, the SELECT age 

requirement ensured that men at risk for the disease were the ones who could enroll. 

Men who had taken, or were taking, vitamin E and/or selenium on their own had to stop 

using these supplements and any multivitamins and use only what is provided by 

SELECT. These supplements are provided to participants free of charge, including a 

multivitamin that does not contain vitamin E or selenium. Past use of these supplements 

did not disqualify men from joining SELECT. 

Participants must have had no history of prostate cancer. Men who joined SELECT also 

must not have had any other cancer, except nonmelanoma skin cancer, in the last 5 years. 

They must have been in generally good health. Many of the 18,000 men who 

participated in another prevention study sponsored by NCI and run by SWOG, known as 

the Prostate Cancer Prevention Trial (PCPT), were eligible to participate in SELECT if 

they had no evidence of prostate cancer. 

Some SELECT study sites are located at Veterans Administration hospitals run by the 

Department of Veterans Affairs. Veterans could enroll at these sites even if they did not 

receive their routine medical care at that hospital. 

7. Could men with benign prostatic hyperplasia (BPH) join SELECT? 

Men with BPH, an abnormal growth of benign prostate cells, could join SELECT 

because BPH is not a cancerous or precancerous condition. In BPH, the prostate grows 

larger and presses against the urethra and bladder, interfering with the normal flow of 

urine. More than half of the men in the United States between the ages of 60 and 70, and 

as many as 90 percent of men between the ages of 70 and 90, have symptoms of BPH. 
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BPH can be treated with four different FDA-approved drugs: finasteride (Proscar®), 

terazosin (Hytrin®), doxazosin (Cardura®), and tamsulosin (Flomax®). Most men 

taking one of these drugs were eligible to participate in SELECT. 

8. What tests were used to determine eligibility for SELECT? 

Tests included a digital rectal examination (DRE) and a prostate-specific antigen (PSA) 

test. During a DRE, a doctor inserts a gloved finger into the rectum and feels the prostate 

gland through the rectal wall to check for bumps or abnormal areas. The PSA test 

measures the level of PSA (a protein produced by the cells of the prostate gland) in the 

blood. PSA levels can rise due to cancer or benign (not cancerous) conditions. Doctors 

often use the PSA test and DRE as prostate cancer screening tests in men who have no 

symptoms of the disease. 

To be eligible for the SELECT trial, participants had to have a DRE that found no signs 

of prostate cancer and a total PSA level less than or equal to 4.0 ng/ml. 

During the trial, DREs and PSA tests are suggested, but not required, on an annual basis 

throughout the course of the study. 

9. Who pays for these tests? 

Physician, medical examination, and general clinic costs, including DREs, are charged to 

the participant in the same way as if he were not part of the trial. These costs may be 

covered by a participant’s health insurance. Financial assistance may be available for 

some men. SELECT, however, pays for follow-up PSA tests. Men with questions about 

insurance coverage or reimbursement should check with their local SELECT site. 

10. Who gets which supplement? 

Men who participate in this study take two capsules a day. Participants were randomized 

(assigned by chance) to receive: 

• selenium and vitamin E 

• selenium and a placebo 

• vitamin E and a placebo 

• two placebos 

Two placebos are used in the trial: one looks and tastes like a selenium capsule; the other 

looks and tastes like a vitamin E capsule. Each placebo contains only inactive 

ingredients. Neither the participants nor the researchers will know who is receiving the 

selenium and vitamin E, or the placebos, until the end of the study. 

DSM Nutritional Products, Inc. (formerly Roche Vitamins, Inc.), Parsipanny, New 

Jersey, is donating bulk vitamin E and vitamin E placebo oils; Tishcon Corporation, 
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Westbury, New York, is currently encapsulating the vitamin E and vitamin E placebo; 

and Sabinsa Corporation, Piscataway, New Jersey, is providing selenium and selenium 

placebo capsules at cost. 

11. How much selenium is being used in SELECT? What risks might be involved? 

The amount of selenium (provided as l-selenomethionine) is 200 micrograms (μg) daily. 

Although the initial results of the Nutritional Prevention of Cancer Trial showed an 

overall decrease in cancer incidence from selenium, a 2003 update reported 17 percent 

more new nonmelanoma skin cancers in the selenium group compared with the placebo 

group (5). It is not clear how these results would apply to men who did not already have 

skin cancer when they enrolled in SELECT, or to men who are not at increased risk for 

skin cancer. 

12. How much vitamin E is being used in SELECT? What risks might be involved?

The amount of vitamin E (provided as dl-alpha-tocopherol acetate) is 400 milligrams 

(mg), which is equivalent to 400 International Units (IU) per day. This dose of vitamin E 

can thin the blood somewhat. Men with uncontrolled high blood pressure were not 

eligible to take part in SELECT because taking this much vitamin E might have increased 

their risk of stroke. 

Vitamin E has been shown to increase the risk of some cardiovascular conditions. In a 

2005 study, men and women with vascular disease or diabetes who took 400 IU of 

vitamin E daily for 7 years had a 13 percent increased risk of heart failure compared with 

participants taking a placebo (6). Heart failure is a condition in which the heart’s ability 

to pump blood is weakened. A 2005 analysis of several studies in which people with 

various medical problems took vitamin E suggested a link between high doses of vitamin 

E (400 IU or more) and increased mortality (7). 

13. What other requirements were there for SELECT participants? 

Upon enrollment, men were asked to have toenail clippings collected to assess selenium 

levels in the body because selenium concentrates in fingernails and toenails. Toenails 

were chosen over fingernails because they take longer to grow and thus contain more 

history of someone’s selenium intake. Blood samples were collected upon enrollment to 

assess levels of vitamin E. 

Upon enrolling, men filled out a questionnaire on their diet and past supplement use. 

There is also an annual questionnaire that asks for updates of some of this information. 

Men do not have to change their diets during this study. Each man is offered a supply of 

a special daily multivitamin, manufactured by The Perrigo Company, Allegan, Michigan, 

that contains no selenium or vitamin E, to take if he chooses. Vitamin E, selenium, 

placebo capsules, and multivitamins will be provided free of charge to enrollees for the 

duration of the study. 
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Participants are asked to return to the study site every 6 months to pick up a 6-month 

supply of capsules. 

14. What are the benefits of participating in SELECT? 

Men involved in SELECT are partners in medical research that may decrease their 

chances of getting prostate cancer. Information learned from this study may also help 

future generations of men avoid this cancer. 

15. What happens if a participant develops prostate cancer while involved in SELECT? 

Participants diagnosed with prostate cancer during the study will be referred for 

treatment, will stop taking the study supplements, and will continue to be followed by the 

SELECT study staff, although less frequently. 

Costs for diagnosis and treatment of prostate problems, prostate cancer, or other medical 

conditions during the study are charged to the participant in the same way as if he were 

not part of the trial. A participant’s insurance will pay for diagnosis and treatment 

according to the plan’s policies. If the participant has no insurance, social services may 

be available at the local level to cover costs for diagnosis and treatment. 

16. What other clinical trials are under way for prostate cancer prevention? 

In addition to SELECT, smaller trials are also being conducted with a variety of agents, 

including a vitamin D analog; soy isoflavones; and lycopene (a plant pigment common in 

tomatoes). 

17. Where is more information about SELECT available? 

In the United States and Puerto Rico, call the National Cancer Institute’s Cancer 

Information Service at 1−800−4−CANCER (1−800−422−6237) for information in 

English or Spanish. People with TTY equipment can call 1–800–332–8615 for 

information in English. In Canada, call the Canadian Cancer Society’s Cancer 

Information Service at 1−888−939−3333 for information in English or French. 

The following Web sites provide additional information: 

• http://www.swog.org—choose the SELECT option 

• http://www.cancer.gov/clinicaltrials/digestpage/SELECT—from the NCI 

• http://www.cancer.gov/newscenter/SELECT—provides images of the prostate, the 

crystalline and chemical structures of vitamin E, and selenium and vitamin E capsules 
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Selected References 

1. American Cancer Society (2005). Cancer Facts and Figures 2005. Atlanta, GA: 

American Cancer Society. Retrieved May 24, 2005, from 

http://www.cancer.org/downloads/STT/CAFF2005f4PWSecured.pdf. 

2. Clark LC, Combs GF Jr., Turnbull BW, et al. Effects of selenium supplementation for 

cancer prevention in patients with carcinoma of the skin. A randomized controlled trial. 

Nutritional Prevention of Cancer Study Group. Journal of the American Medical 

Association 1996; 276(24):1957–1963. 

3. Duffield-Lillico AJ, Reid ME, Turnbull BW, et al. Baseline characteristics and the effect 

of selenium supplementation on cancer incidence in a randomized clinical trial: A 

summary report of the Nutritional Prevention of Cancer Trial. Cancer Epidemiology, 

Biomarkers & Prevention 2002; 11(7):630–639. 

4. Heinonen OP, Albanes D, Virtamo J, et al. Prostate cancer and supplementation with 

alpha-tocopherol and beta-carotene: Incidence and mortality in a controlled trial. 

Journal of the National Cancer Institute 1998; 90(6):440–446. 

5. Duffield-Lillico AJ, Slate EH, Reid ME, et al. Selenium supplementation and secondary 

prevention of nonmelanoma skin cancer in a randomized trial. Journal of the National 

Cancer Institute 2003; 95(19):1477–1481. 

6. Lonn E, Bosch J, Yusuf S, et al. Effects of long-term vitamin E supplementation on 

cardiovascular events and cancer: A randomized controlled trial. Journal of the 

American Medical Association 2005; 293(11):1338–1347. 

7. Miller ER III, Pastor-Barriuso R, Dalal D, et al. Meta-analysis: High-dosage vitamin E 

supplementation may increase all-cause mortality. Annals of Internal Medicine 2005; 

142(1):37–46. 

# # # 

Related NCI materials and Web pages: 

• National Cancer Institute Fact Sheet 2.11, Clinical Trials: Questions and Answers

(http://www.cancer.gov/cancertopics/factsheet/Information/clinical-trials)

• National Cancer Institute Fact Sheet 5.23, Early Prostate Cancer: Questions and 

Answers (http://www.cancer.gov/cancertopics/factsheet/Detection/early-prostate) 

• National Cancer Institute Fact Sheet 5.29, The Prostate-Specific Antigen (PSA) Test: 

Questions and Answers

T

(http://www.cancer.gov/cancertopics/factsheet/Detection/PSA)

• Understanding Prostate Changes: A Health Guide for Men

(http://www.cancer.gov/cancertopics/understanding-prostate-changes)
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• What You Need To Know AboutTM Prostate Cancer

(http://www.cancer.gov/cancertopics/wyntk/prostate)

For more help, contact: 

NCI’s Cancer Information Service 

Telephone (toll-free): 1–800–4–CANCER (1–800–422–6237) 

TTY (toll-free): 1–800–332–8615

LiveHelp® online chat: https://cissecure.nci.nih.gov/livehelp/welcome.asp

This fact sheet was reviewed on 6/13/05