Doubt cast on reliability of prostate cancer test
A study has found that 15 percent of older men with supposedly
normal readings on the widely used PSA test have prostate cancer
anyway - and some even have aggressive tumors.
The findings intensify the dilemma of how to interpret the
test results and how vigorously to treat men with no symptoms.
Some experts think the threshold for what constitutes normal
on the PSA test should be lowered, at least in some cases. But
others say that could lead to unnecessary operations on the
many men whose tumors are so slow-growing that something else
will kill them before the cancer ever does.
“It's a very powerful test, but it's not perfect,”
said Dr. Leonard Gomella, a urologist at Jefferson Medical College
in Philadelphia.
Sixteen percent of American men can expect to be diagnosed
with prostate cancer at some point in their lives.
Yet most such tumors grow slowly, with the death risk at just
3 percent.
Existing screening methods cannot always establish whether
cancer is present and dangerous, so some cases are missed and
others are overtreated with surgery or radiation.
The study, conducted with the help of money and personnel from
the National Cancer Institute, appears in May 27’s New
England Journal of Medicine.
It focuses on the standard screening test for prostate cancer:
the prostate-specific antigen test, or PSA count. The blood
test has been used on millions of men since the late 1980s to
screen those with no symptoms. Many start screening at age 50.
The test measures bloodstream levels of a protein manufactured
by the prostate, a male sex gland. Cancer expands the gland,
pumping out more of the protein and raising the PSA count. A
count of 4 or below (calculated in nanograms per milliliter)
has been widely considered to be normal.
However, the researchers found that 15 percent of 2,950 men
ages 62 to 91 - all with normal PSA counts and rectal exams
- had prostate cancer anyway. And 2 percent of the overall group
had tumors that looked aggressive under a microscope.
“This study adds to information that perhaps the PSA
threshold may be dropped to 2.5 or so,” said Gomella,
the Philadelphia urologist. “The number 4 may not be the,
quote, normal that we look at anymore.”
Lead study author Dr. Ian Thompson of the University of Texas
at San Antonio said the findings justify stronger measures for
some men who have low PSAs but other risk factors, such as prostate
cancer in the family.
However, other patients may decide more often to watch and
wait, since the findings - viewed in another light - add to
the evidence that harmless prostate cancer is quite common,
Thompson suggested.
