PSA Testing for Cancer
A widely used test for prostate cancer may not be as safe as once thought, according to a study released on Wednesday that sparked debate on whether the screening process should be overhauled.
The study found that 15 percent of men with a "normal" reading on the PSA blood test had a prostate tumor. In 2 percent of the men, the cancer was life-threatening.
"There are many men walking around with high-grade prostate cancer who think they don't because they have a normal PSA," Ian Thompson of the University of Texas Health Science Center in San Antonio, the leader of the study, was quoted.
The team, writing in this week's edition of the New England Journal of Medicine, said the finding "underscores the need to consider fundamental changes in the approach to diagnosing prostate cancer." But in an editorial in the Journal, Ballentine Carter of the Johns Hopkins School of Medicine said there were good reasons for not changing the PSA standard.
Normal PSA Results
Carter said there was no evidence, at least not yet, that lowering the definition of "normal" would save lives or help men live longer. "The unexpected detection of cancer at lower PSA levels is more likely to identify disease for which treatment may not only be unnecessary, but also may fail to improve survival," Carter said. The PSA test has been around since 1979 and is increasingly used as a harbinger of prostate cancer, the second-most common cause of cancer death among U.S. males.
The test, credited with cutting that death rate, measures a chemical called prostate-specific antigen in units of nanograms per milliliter of blood. A nanogram is a billionth of a gram. A reading of 4.0 or less is regarded as normal. If the reading is above 4.0, a doctor may recommend the removal of small bits of tissue from the walnut-sized prostate to check for cancer.
Doctors have known for years that the test is not foolproof. Men with low readings can turn out to have deadly tumors, but some prostate cancers can grow so slowly there's little point in treating them -- especially in older men, who are more likely to die of something else. To gauge the risk of having cancer with a normal PSA reading, the Thompson team evaluated volunteers who had been involved in the seven-year study of the prostate drug finasteride. All 2,950 men had been given a placebo instead of the drug, their PSA readings had remained below 4.0, and rectal exams showed no evidence of a swollen prostate.
At the end of the study, biopsies showed that 15 percent of the men had prostate cancer and, among those tumors, 15 percent were in an advanced stage.
The risk varied depending on the PSA reading, although the men found to have cancer were more likely to have a life-threatening tumor if the PSA reading was higher. The problem with lowering the "normal" range from the PSA test is that it would mean a lot more men -- most of them healthy -- would need to have tissue samples taken, which can be painful.
Thompson said the trick was to find better markers that that combine diagnosis and prognosis. "Most men will develop prostate cancer if they live long enough. I don't want to find them. I want to find the ones whose prostate cancer poses some risk," he said.