The Search for Better Tests
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. 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, M.D.,