Researchers are looking for 32,400 healthy men willing to take a dietary supplement every day as part of the world’s largest-ever prostate cancer study. The study was launched this week by the National Cancer Institute (NCI) and the network of cancer researchers called the Southwest Oncology Group (SWOG).

The study will examine whether selenium and vitamin E, two naturally occurring nutrients, can protect men from prostate cancer. It is called SELECT, short for Selenium and Vitamin E Cancer Prevention Trial.

"Previous research with vitamin E and selenium in studies focused on other kinds of cancer suggested that these nutrients might prevent prostate cancer," says Charles A. Coltman Jr, MD, who is leading the study, in a statement issued by the NCI and SWOG. Coltman is chairman of SWOG and director of the San Antonio Cancer Institute.

"[This study] is focused on prostate cancer and, when the study is finished, we will know for sure whether these supplements can prevent the disease," Coltman says.

The large size of this study is necessary to find out whether the selenium, the vitamin E, or both working in combination, prevent prostate cancer, says Howard L. Parnes, MD, NCI chief for prostate and urologic cancer. The study has four groups, and each needs at least 8,100 men in order to have a 96% chance of detecting a preventive effect of 25%, explained Parnes.

"Although prostate cancer is the [second] leading cause of cancer overall in men, after non-melanoma skin cancer, and the second-leading cause of cancer death in men, only 6.6% of men on placebo are expected to develop the disease during the course of the study," Parnes said.

"Therefore, in order to be confident that we will be able to detect a preventive effect if one does exist, it is necessary to enroll a large number of participants," he noted.

Participants will be assigned to one of four groups. One group will take 200 micrograms of selenium daily plus an inactive capsule (placebo), that looks like vitamin E. Another group will take 400 milligrams of vitamin E daily along with a placebo that looks like selenium. A third group will take both selenium and vitamin E. And a final group will be given two placebos.

The study of how nutrients and other substances can prevent cancer is growing, said Fray F. Marshall, MD, professor and chairman of the department of urology at Emory University School of Medicine.

"One of the nice things about this study and chemoprevention is that I can't think of any obviously deleterious effect of this study," Marshall said. Finding effective preventive substances could encourage younger men, who are less likely to think about prostate cancer, to take steps to reduce their risk, Marshall suggested.

The study will accept men age 55 and older. African-American men age 50 and older may enter the study because they have a higher incidence of prostate cancer than other racial and ethnic groups. All men in the study cannot have any history of cancer in the last five years, except for non-melanoma skin cancer.

Men will be recruited at 400 sites around the country and in Canada for the study, which is expected to take 12 years. Each participant will be followed for a total of seven years, so researchers hope to recruit all 32,400 within the first five years of the study, according to the NCI.

The participants will not need to change their diet, but they must stop taking any supplements they buy themselves that contain selenium or vitamin E. Those who want to take a multivitamin can take one that will be provided, without charge, and does not contain selenium or vitamin E.