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The results of
the prostate-specific
antigen (PSA) blood test, used to screen for prostate
cancer, may fluctuate from year to year, according to a new study
reported in the Journal of the American Medical Association (Vol. 289, No.
20: 2695-2700).
In some cases,
levels that were abnormally high returned to normal on their own. This
could have important implications for whether men with an elevated PSA
level should get a prostate
biopsy right away, according to the researchers from Memorial
Sloan-Kettering Cancer Center and the National Cancer Institute.
Usefulness of
Screening Test Still Not Well Defined
Since the
first use of the PSA blood test in the 1980s, doctors have been able to
detect many more cases of prostate cancer at an earlier stage. But the
test is not perfect, and several important questions have yet to be
answered.
For example,
it is not yet known if screening with the PSA test will save lives or
prolong patients' survival. Prostate cancer is thought to be more curable
if detected at an early stage. But some doctors argue that the test may be
detecting some cancers that would never cause symptoms because they are so
slow growing. Treating these cancers, on the other hand, can have side
effects such as impotence or incontinence.
Doctors have
also had a hard time establishing an absolute "cut off" level at
which more testing is needed. Most (but not all) doctors agree PSA levels
below 4 ng/ml are normal, and levels over 10 ng/ml indicate that a
prostate biopsy (in which tissue is removed and examined under a
microscope) is needed.
But a gray
zone exists for levels between 4 and 10 ng/ml. About one in four men whose
PSA is in this range have prostate cancer. Some doctors recommend getting
a biopsy right away. But the biopsy can be uncomfortable and carries a
small risk of infection and bleeding, so other doctors suggest repeating
the PSA test at a later date or using other tests, such as a free-PSA
test, to get a better idea of what may be going on. Other approaches now
under study include watching the trend in PSA levels over time (PSA
velocity), looking at the PSA level in relation to the size of the
prostate (PSA density), or deciding a course of treatment based on the
patient's age.
PSA levels are
also known to be affected by certain conditions, such as inflammation of
the prostate or benign prostatic hyperplasia (BPH), and by medications.
Some previous studies have also suggested that levels may fluctuate over
time within individuals.
Study: PSA
Levels May Vary from Year to Year
In the present
study, researchers examined the PSA levels of nearly 1,000 men over a
four-year period. (The men, all over age 35, had the yearly blood tests
done as part of another study.)
Of the 154 men
who had an elevated PSA (4 ng/ml or higher) on one of the early tests, 30%
returned to a normal level a year later. Similar numbers were found when
the researchers used other criteria to define "abnormal" (such
as using a lower cut-off level of 2.5 ng/ml or using an age-based PSA
cut-off). Overall, nearly half the men who had an abnormal PSA value by
any of the criteria returned to a normal level later on.
Because the
PSA testing was done on samples taken a year apart, the researchers could
not study how quickly the PSA levels may have changed. Still, it was clear
that the levels were fluctuating over time.
"While
PSA testing does lead to the early detection of prostate cancer, a single
abnormal PSA level should be viewed with caution," the authors write.
"A newly elevated level should be confirmed before expensive or
invasive tests, such as a prostate biopsy, are recommended."
Because
prostate cancer generally grows slowly, there would be little harm in
waiting four to six weeks to repeat the test, they conclude. "Because
of the apparent fluctuations in PSA levels over time, this policy would
decrease the number of unnecessary biopsies, but still diagnose men within
a reasonably safe time frame."
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