Prostate PSA Test
The race is on to boost the reliability of the current diagnostic tool and to come up with alternative detection methods.
Discovered in 1986 by Stanford researcher Dr. Thomas Stamey, the PSA blood test for prostate cancer is one of the medical world's most important -- and controversial -- tools. Elevated levels of prostate-specific antigen, a protein made by the prostate gland, can often signify the presence of cancer, but not always. Sometimes a high PSA level simply indicates that the prostate is swollen. The test's inability to be specific has frustrated Stamey. He recently declared the test "all but useless."
Most doctors aren't ready to abandon it. The PSA test has revolutionized the way prostate cancer is detected, with cases being found at much earlier stages than just 20 years ago, when one-third of diagnoses happened when the cancer was already advanced. Researchers, however, are working to come up with better ways of using the PSA test. And others are looking for alternative methods using different protein markers and combinations of markers that could complement the PSA test and make it more accurate.
Prostate PSA Problems
The problem with the PSA test is that it's too sensitive -- and that can lead to unnecessary treatments with nasty side effects, including incontinence and impotence. In a large prevention trial for prostate cancer sponsored by the National Institutes of Health, screening patients with the PSA test produced a high rate of both false positives (no cancer, but test implies its presence) and false negatives (cancer, but test suggests its absence).
Better tests are coming, but bringing them to market will still take years. In the meantime, some researchers have focused on understanding PSA better so it can be used to more accurately detect and diagnose prostate cancer. One suggestion is fee psa levels.
In men whose PSA test levels are moderately high, doctors have begun to also test for a PSA subtype known as free PSA, which shows up in high levels in a noncancerous condition called benign prostatic hyperplasia. If free PSA is low -- making up 20% or less of total PSA -- it could indicate cancer. Other researchers suspect that PSA's rate of increase over time can indicate if a cancer is recurring.
The trouble is that many cases of the disease are mild, where close monitoring instead of treatment at this point may be better. Most men develop cancerous cells in their prostate as they get older, but not all cells will become fast-spreading and life-threatening. "The broader issue for [PSA] technology is to be able to distinguish aggressive cancers from those that aren't," says Gregg Britt, senior vice-president of the Prostate Cancer Foundation. "If we had [better diagnostics], we wouldn't be as concerned about overtreating."
Meanwhile, PSA testing won't disappear, despite the doubts of detractors such as Stamey. But, with any luck, a host of new, sophisticated tests will eventually join it in the doctor's arsenal.