Researchers at the Johns Hopkins School of Medicine
say that how fast the amount of prostate specific antigen
in a man's blood increases is an accurate gauge of tumor
aggression and danger, even when PSA levels are so low as
to not warrant a biopsy.
Findings of a Hopkins study of PSA velocity published
in October's Journal of the National Cancer
Institute may add a new level of predictive accuracy to
prostate cancer testing, the value of which has remained
controversial under currently accepted guidelines, the
investigators say.
"Our data provide a further argument for PSA testing
that begins relatively early in life, when PSA levels are
usually lower and prostate enlargement is not a confounding
factor in diagnosis," said H. Ballentine Carter, the
director of the Division of Adult Urology at Johns Hopkins'
Brady Urological
Institute and lead author of the study. "We would
recommend that men at around age 40, not 50, have their PSA
checked to develop a baseline against which to compare
future changes [velocity], since even a slight rise in PSA
may indicate a potential for cancer down the road."
An estimated 234,460 men in the United States will be
diagnosed with prostate cancer this year, according to the
American Cancer Society.
"The main debate over how to use PSA has centered on
the choice of the level that is used to trigger a biopsy,"
said Carter, a professor at the School of Medicine.
"Lowering the level that triggers a biopsy leads to
detection of more harmless cancers, and higher levels could
miss the opportunity to detect an important cancer early.
We have found that the rate at which a man's PSA rises may
be more important than any absolute level for identifying
men who will develop life-threatening cancer while their
disease is still curable. In addition, PSA velocity could
be a useful method for identifying those men with a
prostate cancer that could be safely monitored — an
approach termed 'active surveillance.'"
PSA is a protein produced by the prostate gland and
found at increased levels in the bloodstream of men with
prostate cancer. In previous research, PSA velocity in the
year before prostate cancer diagnosis has been shown to
identify men who are likely not to be cured by surgery.
However, Carter's latest findings show that PSA velocity
can also identify men with life-threatening disease at a
time when it is still curable.
Using serum samples dating as far back as 1958, frozen
as part of an ongoing randomized health study of men,
Carter and his team determined PSA velocity in 980 of those
study participants (856 without prostate cancer, 104 with
the disease and 20 who died from it) up until May 2005.
They found that the PSA velocity determined at a time when
PSA levels would not have triggered a biopsy were
predictive of death from prostate cancer 20 to 30 years
later.
Those men whose PSA velocity was lower had a 92
percent chance of not dying of prostate cancer 25 years
later, whereas those with a higher PSA velocity had a 54
percent chance of not dying of prostate cancer. The rates
of prostate cancer death were 1,240 in 100,000 for subjects
with a higher velocity compared to 140 in 100,000 for those
with lower velocities.
Carter emphasizes that an important difference between
the current research and previous studies is that the
subjects in the current study were not selected but rather
taken at random from a large ongoing study, thus more
accurately representing the U.S. population.
His research was supported by the Intramural Research
Program of the National Institutes of Health, National
Institute on Aging.
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