Selenium or Vitamin E to Stop Prostate Cancer May Do
More Harm Than Good
National Cancer Institute stops clinical trial from
going forward
Oct. 27, 2008 Selenium and vitamin E supplements,
taken either alone or together, did not prevent prostate cancer in a
study funded by the National Cancer Institute. The data did show,
however, two concerning trends: a small but not statistically
significant increase in the number of prostate cancer cases among the
over 35,000 men age 50 and older in the trial taking only vitamin E, and
a small, but not statistically significant increase in the number of
cases of adult onset diabetes in men taking only selenium.
The Selenium and Vitamin E Cancer Prevention Trial
(SELECT), funded by the National Cancer Institute (NCI) and other
institutes that comprise the National Institutes of Health has been
closed.
Although, the news release from the NCI said,
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.
The Southwest Oncology Group (SWOG), an
international network of research institutions, coordinates SELECT at
more than 400 clinical sites in the United States, Puerto Rico, and
Canada.
SELECT participants are receiving letters
explaining the study review and telling them to stop taking their study
supplements.
Participants will continue to have their health
monitored by study staff, which may include regular digital rectal exams
and PSA (prostate-specific antigen) tests to detect prostate cancer.
Investigators intend to follow the participants for about three years to
determine the long-term effects of having taken either supplement or
placebo and to complete a biorepository of blood samples that will be
used in extensive molecular analyses to give researchers a better
understanding of prostate cancer, other cancers, and other diseases of
male aging.
This additional data collection is a vital part of
the study, says NCI.
Neither the men nor their physicians know which
supplements or placebos the men have been taking, a procedure known as
blinding or masking.
As followup of the SELECT participants continues,
the participants will continue to be blinded. A blinded followup may
avoid unintentional bias and potentially false conclusions. However, at
the request of a participant, they will be informed which supplement, if
any, they received.
SELECT was always designed as a study that would
answer more than a single question about prostate cancer, said Eric
Klein, M.D., a study co-chair for SELECT, and a physician at the
Cleveland Clinic. 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.
SELECT was undertaken to substantiate earlier,
separate findings from studies in which prostate cancer was not the
primary outcome: a 1998 study of 29,133 male smokers in Finland who took
vitamin E to prevent lung cancer surprisingly showed 32 percent fewer
prostate cancers in men who took the supplement, and a 1996 study of
1,312 men and women with skin cancer who took selenium for prevention of
the disease showed that men who took the supplement had 52 percent fewer
prostate cancers than men who did not take the supplement.
Based on these and other earlier findings, in 2001,
men were recruited to participate in SELECT. They were randomly assigned
to take one of four sets of supplements or placebos, with more than
8,000 men in each group. One group took both selenium and vitamin E; one
took selenium and a vitamin E placebo; one took vitamin E and a selenium
placebo; and the final group received placebos of both supplements.
It should be noted that in 2003, while SELECT was
recruiting men, a different SWOG-sponsored study reported that the drug
finasteride reduced the incidence of prostate cancer by 25 percent. When
this was discovered, men on SELECT were informed and allowed to take
finasteride. Finasteride has not yet been approved by the U.S. Food and
Drug Administration for prostate cancer prevention.
Except for skin cancer, prostate cancer is the most
common type of cancer in men in the United States. In 2008, there will
be an estimated 186,320 new cases of prostate cancer and 28,660 deaths
from this disease in the United States. 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, said
NCI director John E. Niederhuber, M.D. 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.
SELECT has been funded by NCI for $114 million,
with additional monies from the National Center for Complementary and
Alternative Medicine, and with substudies funded and conducted by the
National Heart, Lung and Blood Institute, the National Institute of
Aging and the National Eye Institute at NIH. The substudies were
evaluating the effects of selenium and vitamin E on chronic obstructive
pulmonary disease, the development of Alzheimer's disease, and the
development of macular degeneration and cataracts, and will continue
without participants taking study supplements. An NCI-funded substudy is
looking at the effects of the supplements on men who developed colon
polyps.
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, said Laurence H. Baker, D.O., chairman of the Southwest
Oncology Group. SELECT investigators are analyzing the data and will
submit the analysis for publication in a peer-reviewed medical journal.
The Southwest Oncology Group (www.swog.org)
is one of the largest cancer clinical trials cooperative groups in the
United States. Funded by research grants from the National Cancer
Institute, part of the National Institutes of Health, the group conducts
clinical trials to prevent and treat cancer in adults, and to improve
the quality of life for cancer survivors. The group's network of more
than 5,000 physician-researchers practice at nearly 550 institutions,
including 18 National Cancer Institute-designated cancer centers.
Headquartered in Ann Arbor, Mich. (734-998-7130), the group has an
operations office in San Antonio, Tex. and a statistical center in
Seattle, Wash.
NCI leads the National Cancer Program and the NIH
effort to dramatically reduce the burden of cancer and improve the lives
of cancer patients and their families, through research into prevention
and cancer biology, the development of new interventions, and the
training and mentoring of new researchers. For more information about
cancer, please visit the NCI Web site at
http://www.cancer.gov or call NCI's Cancer Information Service at
1-800-4-CANCER (1-800-422-6237).
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boomers
Oct. 27, 2008 Selenium and vitamin E supplements,
taken either alone or together, did not prevent prostate cancer in a
study funded by the National Cancer Institute. The data did show,
however, two concerning trends: a small but not statistically
significant increase in the number of prostate cancer cases among the
over 35,000 men age 50 and older in the trial taking only vitamin E, and
a small, but not statistically significant increase in the number of
cases of adult onset diabetes in men taking only selenium.