A popular but controversial prostate cancer test can help identify high-risk tumors, improving doctors' ability to predict which patients need aggressive treatment, a new study has found.
In recent years, some experts have questioned the reliability of the test, which measures blood levels of an enzyme called prostate specific antigen, or PSA.
But the latest work, which appears in today's issue of the New England Journal Of Medicine, looked at PSA from a different perspective than earlier efforts.
Instead of studying one-time measurements of PSA, the scientists measured how rapidly the level rose when the test was repeated over a period of months or years. The result: Among men with prostate cancer, those whose PSA rose two or more points in a year were most likely to die.
While some doctors already use this measurement, known as "PSA velocity," it has not become a medical standard. The new study could change that.
"PSA velocity is more important than the absolute PSA level," said one of the study's authors, Dr. William Catalona, a urology professor at Northwestern University. "My guess is that this is going to be incorporated into clinical practice pretty quickly."
The PSA enzyme normally stays within the prostate gland. But when the prostate is invaded by cancer, PSA leaks into the bloodstream.
Over the past 15 years, doctors have increasingly focused on blood levels of PSA to detect prostate cancer. A PSA level above 4 nanograms per milliliter of blood has generally been used as the danger point.
But critics note that some men with levels above 4 don't have cancer, while others with lower levels do, calling into question the test's accuracy.
Last month, another scientific group reported that the PSA produced a high number of false negatives - more than 15 percent of men in their study with "normal" PSA levels turned out to have prostate cancer.
But the latest research reaffirms the test's importance as a cancer screen.
"People have questioned the value of PSA, which is unfortunate," said Dr. Judd Moul, chairman of the Duke University urology department. "PSA has saved thousands of men's lives."
Several doctors noted that the two studies do not necessarily conflict. Prostate cancer patients with low PSAs can also exhibit high PSA velocity.
James O'Brien, 45, an auto parts store manager in suburban Chicago, is a good example. In October, his PSA reading was 2.4.
Six months later, another test showed his PSA had risen to 3.7. Extended over a year, his PSA velocity was 2.6.
Although his absolute PSA was still below the traditional warning level of 4, his doctor ordered a biopsy, which revealed prostate cancer. In April, Catalona performed prostate surgery, which apparently was successful.
"If I would have waited [to have a biopsy], who knows?" O'Brien said.
The new study, which lasted from 1989 to 2001, followed 1,095 prostate cancer patients, all of whom had surgery. Researchers measured PSA velocity around the time of diagnosis and surgery and found that patients whose PSA rose by 2 or more points a year were 10 times as likely to die of cancer as those with smaller increases.
About 200,000 American men are diagnosed with prostate cancer annually, and 30,000 die.
In recent years, doctors have discovered that not all prostate cancer patients need aggressive treatment. In many men, the tumors are small and grow slowly, posing relatively little risk.
For patients in this group, doctors are increasingly opting for an approach called "watchful waiting." Instead of performing surgery, which can have severe side effects such as impotence, they carefully monitor patients for signs that the cancer is spreading.
But doctors have long wanted a test that could accurately determine which men were the best candidates for this monitoring. "Everybody has been looking for a way to differentiate harmless cancers from dangerous ones," said Catalona.
PSA velocity will help doctors make this distinction. "It helps to narrow down which tumors are the troublemakers," said Dr. Mario Weinberger, a Johns Hopkins University oncology and urology professor who wrote an editorial accompanying the study.
For patients with a high velocity, doctors will now be more willing to use aggressive treatments, including surgery, radiation and chemotherapy, said Catalona.
To better track PSA velocity, some doctors think that men should begin having the tests at age 40, instead of 50. By starting younger, doctors can more precisely track PSA trajectory.
"We've misused the PSA test," said Dr. Anthony D'Amico, a professor of radiation oncology at the Harvard Medical School and one of the paper's authors. "We should be looking at the trend."
Catalona said earlier screening would likely cut the prostate cancer death rate. "If men measure PSA earlier and more regularly, we'll be detecting these cancers earlier," he said. "And that will save lives."