An initial independent review of data from a study looking at whether selenium and vitamin E supplements prevented prostate cancer found they had no benefit, taken either together or alone.
The review of data from the Selenium and Vitamin E Cancer Prevention Trial (SELECT) was funded by the National Cancer Institute (NCI) in the US and other institutes from the National Institutes of Health in the US.
SELECT was started to corroborate findings from studies on other primary cancer outcomes that found significantly fewer prostate cancers in men who took either Vitamin E or selenium supplements.
SELECT started in 2001 and eventually recruited more than 35,000 male volunteers over 50 years The men were randomly assigned to one of four groups: (1) real selenium and real vitamin E, (2) real selenium and vitamin E placebo , (3) selenium placebo and real vitamin E, and (4) placebo selenium and placebo vitamin E.
The study was set up as a double blind trial; that is neither the participants nor the doctors administering the treatment knew which group they were in.
The initial analysis also found two small but disturbing trends, neither of which is statistically significant, but all the men are being told to come off the supplements and continue to be monitored.
There was a small and statistically insignificant rise in the number of prostate cancer cases among the men taking only vitamin E, and a small and statistically insignificant rise in number of type 2 diabetes cases among men taking only selenium.
The researchers said in a statement that:
"Because this is an early analysis of the data from the study, neither of these findings proves an increased risk from the supplements and both may be due to chance."
Letters are being sent to the participants explaining these initial findings and telling them to stop taking their supplements. Study staff will continue to monitor the participants' health for three years of follow up and this may include regular digital rectal exams and tests for PSA (prostate-specific antigen).
The men continue to be blinded to prevent potential bias, but if a participant wishes to know which group he was in and which supplements he received he will be told.
An international network of research institutions called the Southwest Oncology Group (SWOG) coordinates SELECT at more than 400 clinical sites in the United States, Puerto Rico, and Canada.
During the follow up the researchers will also collect blood samples to put in a biorepository. This is another important objective of the study and will provide a bank of samples that researchers can analyse to better understand prostate and other cancers and other diseases of older men.
While the SELECT study was recruiting participants in 2003, another SWOG-sponsored study found that the drug finasteride reduced the incidence of prostate cancer by 25 per cent. The men on the SELECT study were told about this and offered the option to take finasteride, which has not been approved in the US as a prostate cancer prevention drug.
Dr Eric Klein, a study co-chair for SELECT, and a physician at the Cleveland Clinic, said:
"SELECT was always designed as a study that would answer more than a single question about prostate cancer."
"As we continue to monitor the health of these 35,000 men, this information may help us understand why two nutrients that showed strong initial evidence to be able to prevent prostate cancer did not do so," he added.
Prostate cancer is second only to skin cancer as the most common form of cancer among men in the US where in 2008 estimates suggest over 186,000 new cases will be diagnosed and over 28,600 men will die of the disease.
NCI director Dr John E Niederhuber said:
"Finding methods to prevent and treat prostate cancer remains a priority for the NCI, and with the aid of new molecular diagnostic tools and applications, we hope to continue to make headway in reducing deaths and new cases of this disease."
"The science of cancer prevention is also leading toward individualized, molecular prevention, in which we will calculate risk and design preventive steps based on an individual's genome," he added.
The SELECT investigators are continuing with the data analysis and intend to publish the final results in a peer-reviewed medical journal.
Dr Laurence H Baker, chairman of the Southwest Oncology Group, said:
"The SELECT trial owes a tremendous debt to our volunteers, the thousands of men who offered their time and enthusiastic participation, all in the interest of a future when prostate cancer can be prevented."