The study found that 15 percent of men with a "normal" reading on the PSA blood test had prostate cancer and that the disease was life threatening in 2 percent of the men.
"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 study's lead researcher, told Reuters.
To assess the risk of having cancer with a normal PSA reading, Thompson and the other researchers conducted prostate biopsies on 2,950 study volunteers aged 62 to 91 who had normal PSA readings 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 men, 15 percent had tumors that were in an advanced stage.
The study's authors concluded the new research "underscores the need to consider fundamental changes in the approach to diagnosing prostate cancer."
The PSA blood test costs about $30 to $50 and measures the level of a blood protein called prostate-specific antigen. Higher PSA levels can indicate an infection, benign forms of prostate disease, or cancer.
"This study adds to information that perhaps the PSA threshold may be dropped," Dr. Leonard Gomella, a urologist at Jefferson Medical College, told the Associated Press.
However, an editorial written by Johns Hopkins School of Medicine professor Dr. Ballentine Carter in this week's Journal cautions against changing the current standard. Carter said there was not yet evidence that flagging lower levels of PSA protein for additional screening would save lives.
"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.
Lowering the "normal" range for the PSA test would mean a lot more men -- most of them healthy -- would need to have a biopsy that more accurately detects the cancer.
Another factor complicating the debate over PSA tests is that some of prostate cancers grow so slowly that older men with the disease are more likely to die of something else.
About 230,900 men in the United States will be diagnosed with prostate cancer in 2004 and about 29,900 men will die from the disease, the American Cancer Society estimates.
Thompson said the key is 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 told Reuters.