Test Misses Tumors, Study Finds
The widely used PSA blood test,
designed to look for early signs of prostate cancer, misses 82
percent of tumors in men under 60, according to a study released.
The prostate-specific antigen test
missed 65 percent of cancers in older males, the study, published
in the New England Journal of Medicine, found.
Dr. Rinaa Punglia of Harvard Medical
School and her team said the accuracy of the test has been overrated
because doctors do not routinely confirm what seems to be a healthy
reading on the test.
Currently, a PSA level of 4 or
under is considered healthy.
The American Cancer Society says
a level above 4 but less than 10 means a 25 percent chance of
having prostate cancer. If the level goes above 10, the cancer
risk is more than 67 percent.
Punglia's team recommended lowering
the "healthy" reading to 2.6 -- even though many more men who
do not have prostate cancer will have to undergo painful biopsies
to verify they do not have cancer.
The PSA test, approved in 1986,
measures levels of prostate-specific antigen, a protein produced
by prostate cells and over-produced by prostate tumors. The test
has been credited with detecting prostate cancer in its early
stages 80 percent of the time.
But the Punglia team evaluated
6,691 volunteers at the Washington University School of Medicine
in St. Louis and found that men under 60 with prostate cancer
had a "healthy" PSA reading 82 percent of the time.
Only 2 percent of men get a "false
positive" -- meaning they have a PSA of above 4 even though they
do not have cancer.
For older men, the test missed
65 percent of the tumors and was wrong in 12 percent of the men
who had a suspicious reading of 4.1 or above.
Lowering the "healthy" threshold
to 2.6 would catch more tumors, the researchers said.
For men under 60, that would double
the tumor detection rate to 36 percent, while the ratio of healthy
men who would be subjected to an unnecessary biopsy would rise
from 2 percent to 6 percent.
The Prostate Cancer Coalition said
it already advocates checking men with lower PSA levels.
"While small fluctuations in the
PSA reading for men over 60 can be often be a sign of a false
positive, those same small changes in younger men can often be
a sure sign of cancer," coalition spokesman Jamie Bearse said.
"The National Prostate Cancer Coalition
uses a 2.5 PSA rating as the bar for men under 60," he added.
"While the study is encouraging, NPCC would suggest that the reading
of 2.5 be set even lower, a 2.0, for African-Americans under 60
because black men are at greater risk for the disease."
But in an editorial in the Journal,
Fritz Schroder and Ries Kranse of the Erasmus Medical Center in
Rotterdam, Netherlands, said there was no conclusive evidence
showing the PSA screening test actually reduces the risk of death
from prostate cancer without reducing a man's quality of life.
Prostate cancer is usually a slow-growing
cancer and often does not require any treatment. However, prostate
cancer kills about 29,000 Americans each year and is the second
most common cancer killer of U.S. men, after lung cancer.
Reference Source 89