An influential government panel today recommended against routinely screening healthy men with a blood test for prostate cancer. The U.S. Preventive Task Force said that the widely used PSA test leads to more harm in treatment side effects than good in saving lives.
“For men aged 50 to 69 years, the evidence is convincing that the reduction in prostate cancer mortality 10 years after screening is small to none,” said the task force in a draft recommendation statement issued today (Oct. 7), after reviewing five major studies on the issue. In a previous statement, the panel said there was not convincing evidence to recommend in favor of or against PSA tests for men under age 75.
The tests detects many cases of prostate cancers growing so slowly they will never shorten a man's life or negatively affect his health, the panel said. And there are harms associated with PSA screening tests, such as unnecessary biopsies and the negative psychological effects of persistently worrying about prostate cancer.
Researchers said they are unsurprised by the new recommendation.
“We all knew what the results were going to be,” said Dr. Andrew Vickers, a PSA researcher at Memorial Sloan-Kettering Cancer Center in New York City.
“The way the screening is done in the U.S. is very irrational. I think it's very understandable to say we need to stop doing what we're doing,” Vickers said.
But that doesn't mean, in Vickers view, that PSA testing does not do any good. For instance, he said, at the general population level, PSA screens can be “a very strong predictor of which cancers will be fatal.”
PSA: A blood test that catches tumors early
Prostate cancer behaves so differently from other cancers that 20 years after doctors started using the PSA, or prostate-specific antigen, test, researchers still can't say exactly how much good, or harm, the test does.
A study published online last week in the Annals of Oncology showed mortality from prostate cancer in the U.S. dropped by an estimated 23 to 38 percent, depending on the age group examined, in the years 2002 through 2006, as compared with 1985-1989 — just before the PSA test was widely adopted. (The study was not one of those reviewed by the panel.)
“As a urologist, I feel that PSA testing has really saved a lot of lives in this country,” said Dr. Judd Moul, director of the Duke Prostate Center in Durham, N.C.
The National Cancer Institute lists prostate cancer as the second most common cause of cancer death in men. An estimated 217,730 U.S. men received a prostate cancer diagnosis in 2010, and an estimated 32,050 men died from the disease that year, the panel said.
But because the PSA test catches so many tumors in early stages, it “has opened up a pandora's box in cancers,” leaving some wondering what to do when they have a positive result, Moul said.
Indeed, other findings of the new study imply PSA testing has caught many tumors that would never have killed men in the first place. Comparing 1985-1989 with 2002-2006, the study found that among men between the ages of 40 and 64, mortality declined by 31 percent, while new prostate cancer diagnoses rose 175 percent.
And among men between the age of 65 and 74, mortality declined 38 percent, while new diagnoses rose 44 percent, the study showed.
The PSA test measures proteins produced by the prostate gland that are circulating in the blood. A healthy prostate produces low levels of these proteins, and a high level of PSA in the blood may indicate disease, according to the National Cancer Institute.
Before PSA testing, men were often diagnosed with prostate cancer in advanced stages. Moul said in the pre-PSA testing era, about one-fifth men who were diagnosed with prostate cancer already had metastases, advanced cancer, in their bones. “Today, the chance of finding [prostate] cancer spread to the bone is only 1 to 2 percent,” Moul said.
The authors of the study said its unclear whether mortality declines due to PSA screening will continue. “It cannot be excluded that PSA testing associated mortality declines will occur in the future — the more time this should take, the more likely it is that such decline will affect [men of] older ages,” they wrote.
But prostate cancer can take a decade or more to grow into tumors that threaten a man's life, said Dr. Durado Brooks, director of prostate and colorectal cancers at the American Cancer Society. Because the cancer often strikes later in life, many men diagnosed with early stages of prostate cancer would have died from other causes.
A slow growing, confounding cancer
“In some instances, we don't know if [a patient is] alive because we treated him, or in spite of the treatment,” Brooks said. And treatment, Brooks said, can lead to sexual dysfunction and urinary incontinence.
Trying to determine where PSA saved lives, and where it has not takes complicated mathematical models, according to Vickers.
“It would be very difficult to attribute all of this change in mortality to PSA,” Vickers said.
New treatments, including robotic surgery and advances in radiation therapy techniques, followed the PSA testing trend and have also saved lives, Brooks said, even though these advances have not been adopted evenly across the U.S.
Still, PSA testing has proved itself a useful tool, said Vickers. “It's really obvious that there's been a big change in prostate cancer mortality, as compared to breast cancer,” he said.
It's just a matter of knowing when to test.
“In the U.S. a very high proportion of PSA testing is done in men who have very little benefit of it,” Vickers said. “The reason why the older men are being screened instead of the younger men are because they are already in the doctor's office. It's extraordinarily skewed toward older men.”
Rather than ration PSA testing to the most at-risk groups, Moul said there is a new push from the American Urological Association to screen all younger men for baseline levels. Moul said taking a baseline PSA score at age 40 would let doctors strategically follow men whose levels show they are more likely to develop deadly tumors.
In 2008, a review of prostate cancer studies prompted the task force to recommend against PSA screening in men over age 75. “The evidence is convincing that for men aged 70 years and older, screening has no mortality benefit,” the panel reiterated today.
“Maybe it's not the PSA test that's bad,” Moul said. “It's how we use it — can we use the tool more intelligently?”
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