About 20 years ago, there was a
revolutionary development in prostate cancer diagnosis.
Researchers at Stanford University School of Medicine
suggested that a simple blood test measuring the level
of a protein called prostate specific antigen (PSA) could
detect prostate cancer. This quickly led to widespread
testing and the growth of a billion-dollar
screening industry.
Times have changed, and a more
recent study at Stanford has led the same researchers
to refer to PSA testing as "all but useless." Over the
years, the association between high PSA and prostate
cancer significantly declined, and today an elevated
PSA is most likely a sign of benign
prostate enlargement.
Are They Sure?
To learn more about PSA testing,
I spoke with Kathryn L. Taylor, PhD, assistant professor
in the department of oncology at the Lombardi Comprehensive
Cancer Center of Georgetown University Medical Center in
Washington, DC. Dr. Taylor is the principal investigator
of a National Cancer Institute-funded study to evaluate
patient education that is designed to provide detailed
screening and treatment-related information and to clarify
patient preferences and values, ultimately assisting men in
making an informed screening decision.
She told me that although there are many
difficulties with the PSA test, the issue is far
from resolved.
About the Study
Researchers examined the results
of more than 1,300 prostate tissue samples collected
at Stanford University over the last 20 years. They
divided them into four five-year periods between 1983
and 2004, and compared the occurrence of cancer with
the results of clinical findings, including PSA levels
and rectal examinations.
They discovered that the correlation
between PSA levels and largest prostate cancers had
dropped dramatically. Twenty years ago, there was a
significant relationship between high PSA value and
size of the largest prostate cancer. In the first five-
year period, PSA testing had a 43% predictive ability,
in comparison with just 2% in the past five years.
These results were published in the
October, 2004 issue of The Journal
of Urology.
Test Results with Ambiguous Meanings
Why the drastic change? Stanford
researchers speculate that so many men in this country
have now been screened for prostate cancer that it is
possible that most of the major prostate cancers have
been detected and removed. As a result, an elevated PSA
is now more likely to be a sign of an enlarged prostate --
a condition that affects the majority of men as they age,
causing urine flow to be weaker and slower. Prostatitis
(an inflammation of the prostate gland) also can lead to
an elevated PSA.
The problem is that PSA test results
often are ambiguous and can have profoundly
serious ramifications...
False-positive results (that suggest
a person has cancer when he does not) are common and can
lead to uncomfortable, invasive biopsies and
unnecessary anxiety.
Although testing may detect early-stage
prostate cancers, it is by no means certain that this leads
to improved survival rates. Left undetected and untreated,
a slow-growing prostate tumor might never affect an older
man's health.
Potential complications of prostate
surgery include a 20% to 70% risk of impotence and a
15% to 50% chance of severe incontinence (and a larger
chance of less severe incontinence).
Making an Informed Choice
Many major medical organizations that
specialize in cancer do not advocate routine testing for
prostate cancer. Those that do -- the American Cancer
Society and the American Urological Association --
recommend only that PSA and digital rectal examination
(DRE) be offered and discussed as a yearly option to
men once they reach age 50.
According to Dr. Taylor, men
must carefully weigh the risk that they may be
treated unnecessarily, versus the benefit that
prostate cancer could be detected and treated early
to reduce their chance of dying from this disease.
Talk to your doctor, taking into account individual
risk factors, such as a family or personal history of
prostate cancer. In this way, you can make an informed
decision about whether or not you want to be tested.
Questions to explore include...
Would you feel better knowing or not
knowing that you have prostate cancer?
What will you do if your screening result is
abnormal? Will you choose to have a biopsy or not?
What will you do if the diagnosis is cancer?
If the tumor does not appear to be large, aggressive or fast
growing, will you undergo active treatment or opt for the wait-
and-see monitoring approach known as "watchful waiting"?
Looking Toward the Future
In the meantime, research continues.
Scientists are seeking ways to fine-tune the PSA test,
and they are searching for a new and more accurate
prostate cancer marker.
To ascertain whether PSA and DRE
testing reduces deaths from prostate cancer, the National
Cancer Institute is conducting the Prostate, Lung,
Colorectal, and Ovarian (PLCO) Cancer Screening Trial.
Results will be available in five years.
To keep up with the latest information
on prostate cancer detection and treatment, visit the
Web sites of the American Cancer Society (www.cancer.org)
and the National Cancer Institute (www.cancer.gov). Also,
remember that the pharmaceutical industry, like any other
industry, is driven primarily by money. Facilities
invested in outdated technology may wait to upgrade
until the absence of newer technology is felt in their
pocketbooks. Do your homework so you know all of the
options available for treatment even if they are not
available at your local hospital.
Sources...
Kathryn L. Taylor, PhD, assistant professor,
department of oncology, Lombardi Comprehensive Cancer
Center, Georgetown University Medical Center,
Washington, DC. American Cancer Society, www.cancer.org
National Cancer Institute, www.cancer.gov
