Every year, millions of men undergo screening for prostate cancer. This disease, which strikes one out of every six men, is very curable in its early stages. But, say some doctors, early detection of prostate cancer is doing more harm than good.
"We're over-diagnosing it, and we're over-treating too many men," said Richard Ablin, a professor of immunobiology and pathology at the University of Arizona College of Medicine. "The way the test is used today is wrong."
Meanwhile, a new study out today finds that screening for prostate cancer, at least in Swedish men ages 50 to 65, can cut death rates from the disease by nearly half. However, even the researchers involved in this study note, in the journal Lancet this week, that "the risk of over-diagnosis is substantial."
The prostate is a walnut-sized gland nestled beneath the bladder. Prostate cancer is one of the most common causes of cancer deaths, killing 1 out of every 35 men. Catching the cancer before it spreads can improve a patient's chances of being alive five years later from 30 percent to almost 100 percent. [Why Can't We Cure Cancer?]
That's where prostate screening comes in. Prostate cells produce a protein called prostate-specific antigen, or PSA. A blood test can catch elevated levels of PSA, which can be a sign of prostate cancer. Most doctors consider more than 4 nanograms of PSA per milliliter of blood to be a red flag.
The problem, according to Ablin and other critics of PSA testing, is that PSA isn't cancer-specific. Benign conditions like prostate enlargement or inflammation can also boost PSA levels.
That means the test isn't a reliable marker of prostate cancer on its own. A 1997 study, published in the journal Cancer, found that of men with PSA levels greater than 4, 65 to 75 percent were cancer-free. And in 2004, researchers reported in the New England Journal of Medicine that 15 percent of men with PSA levels below 4 - the supposed all-clear point - actually had cancer.
In perhaps the most damning blow to PSA screening, two large 2009 studies, one in the United States and one in Europe, found limited benefits to early detection. The U.S. study found that annual PSA screening plus a digital rectal exam (in which a doctor feels the patient's prostate through the rectal wall, looking for abnormalities), had no effect on prostate cancer deaths during the next 11 years.
The European study found that PSA testing every four years did reduce cancer deaths by 20 percent. But for every life saved, doctors had to screen 1,410 men and put 48 through unnecessary treatment.
Those treatments come with a price, Ablin said. Surgical removal or radiation of the prostate can cause incontinence and impotence. Quality-of-life implications aside, those side effects are also expensive, as men may need to rely on erectile dysfunction drugs and adult diapers for years after treatment.
As flawed as the PSA test may be, it can still be useful, say some doctors.
"Yes, it's not a perfect test, no, we shouldn't demonize it," Stuart Holden, director of urology at Cedars-Sinai Medical Center and the medical director of the Prostate Cancer Foundation, told LiveScience. "The number of cases at the time of diagnosis which are metastatic - in other words, incurable - used to be 70 to 80 percent of the cases that we'd see. Now it's 15 to 20 percent, and that's strictly because PSA has led us to an early diagnosis."
The test is also a valuable measure of reoccurrence after a cancer diagnosis, Holden said.
One thing everyone agrees on is that prostate screening could be better. Researchers, including Ablin, are looking for cancer-specific chemicals that could predict not only the presence of cancer, but its likelihood to spread. Tests that measure changes in PSA, rather than absolute levels, could be useful. So could snippets of prostate-specific ribonucleic acid (RNA) called PCA3 that show up in high levels in prostate tumors. PCA3 can be detected with a simple urine test.
Holden and other researchers at Cedars-Sinai and Johns Hopkins University are also beginning a study that will examine tissue samples from men diagnosed with prostate cancer who choose a "wait-and-see" approach to treatment. The researchers hope to follow the men closely to determine whose cancer spreads and why.
As the PSA controversy plays out, some organizations, like the American Urological Association, continue to recommend annual screening after age 40. Others, like the American Cancer Society, suggest discussing the risks and benefits of the test with a doctor after age 50.
"The people that are best informed about this are the doctors that live in this world and deal with it on a day-to-day basis," Holden said at an April 20 roundtable on prostate cancer in Washington, D.C. "I don't think there's any substitute for the doctor-patient relationship, nor will there ever be."