Why are we so interested in finding new tests for prostate cancer?
There are lots of reasons — nearly 35 million of them. That's
the number of men — just in the United States — who have a
PSA test each year. Of these men, "well over a million undergo
a costly, potentially painful, and most certainly anxiety-provoking
biopsy," comments Alan W. Partin, M.D., Ph.D., the David Hall
McConnell Professor and Director of Urology. "And yet, only
250,000 of these men are found to have prostate cancer. This means
that most men undergoing a prostate biopsy do not have cancer."
The PSA test has what scientists
call "good sensitivity" — it is good at detecting
cancer. But it has “poor specificity" —manymen have to
get a biopsy before cancer can be ruled out. More numbers: "With
all of these men who have no cancer found, yet who have an abnormal
PSA test, it's estimated that more than 20 million American men
have had at least one negative prostate biopsy."
The biopsy found no cancer. But for
most men, the issue doesn't just rest there. The spectre of cancer
has been unleashed, and it haunts them — maybe only slightly
or maybe quite a bit. Is cancer there, hiding, and the doctor missed
it? Or do some men just have an abnormal PSA? "New tests are
urgently needed," says Partin.
Scientists at the Brady Urological
Institute are working hard to find them, and we've got three promising
candidates. One of them, EPCA-2, is covered in
this story. Two others — one, called a GSTPi
test, used on prostate tissue, and a urine test, which looks for
a marker called PCA3 — are being investigated clinically.
Partin is heading both of these investigations.
35 million American men
have a PSA test each year.
More than a million of these
men undergo a biopsy — but
only 250,000 are found to have
The GSTPi test can detect very small
numbers of cancer cells — so small that they may not be visible
to a pathologist looking at prostate biopsy samples under a microscope.
GSTPi is a gene. Several years ago, Brady scientist William G. Nelson,