Most men diagnosed with prostate cancer in the past two decades never needed to know they had the disease, leading many to treatment that can do more harm than good, according to a new study.

The findings, published in Monday's Journal of the National Cancer Institute, found that since a blood test became the standard way to screen for prostate cancer, an additional 1.3 million men have been diagnosed with the disease. But because many men are diagnosed with cancer that will not cause symptoms and will not kill them, the screening tests save few lives, the authors conclude.

The findings have reignited a long-simmering debate in medical circles on the merits of the blood test, known as prostate-specific antigen screening, or PSA. The study also flies in the face of such efforts as prostate cancer awareness month and radio ads touting free screening tests, and challenges the notion that when it comes to cancer, the earlier it's found the better the prognosis.

"Just the diagnosis of cancer causes a fair amount of anxiety. No one wants to be given that diagnosis needlessly," said Dr. H. Gilbert Welch, a researcher from the Dartmouth Institute for Health Policy & Clinical Practice, and the study's lead author. "The bigger problem is being given treatment that can't help you, but all of our treatments can hurt you."

Some prostate cancer experts reacted strongly to the study. One said the paper is irresponsible and misleading, leaving men to sift though conflicting messages about their health.

"If you are a healthy man with a more than 10- to 15-year life expectancy and you don't want to die from prostate cancer, you should have PSA testing; intelligent testing and treatment could save your life," said Dr. Patrick C. Walsh, university distinguished service professor of urology at Johns Hopkins. "I can't believe this article ever got published."

Welch said he is not trying to discourage PSA testing - although he said he would not get the test himself. Rather, patients should understand the disease, the ramifications of screening and the problems that can come from treatment, which include urinary incontinence and impotence.

"It's a close call," he said. "This thing has a real downside. It has a huge population impact in the number of men who have been told they have prostate cancer, and that's a harm. And we need to weigh that harm against any benefits."

Prostate cancer is the second-leading cause of cancer death in men, behind lung cancer. But the concept that people can have cancers that never end up hurting them is not well-understood by the public, Welch said. Also, doctors don't have a way to tell which cancers will progress to be lethal and which won't.

He said doctors should initiate conversations with their patients about the impact of early diagnosis and discuss the risks that come with treatment.

Many physicians are reluctant to relay this message to patients, wrote Dr. Otis Brawley, chief medical officer at the American Cancer Society, in an editorial accompanying the study. "Many screening advocates (both physician and lay) have had difficulty accepting that some cancers are not going to progress and cause symptoms or death within the lifetime of the patient," he said.

Brawley also said that prostate cancer's much publicized early-detection message has gone too far with radio commercials encouraging all men to get screened. Such a commercial "plays to our fears and prejudices," he wrote.

Meanwhile, some doctors encourage screening simply because they stand to gain financially, Brawley said.

Welch called such advertisements "obscene."

"The advertising is, by its definition, persuasive," he said. "You've got to have a more balanced presentation. ... Doctors know that a certain number of patients will need biopsies and that will bring revenue. A certain number will need treatment and that brings in revenue."

Using data from the National Cancer Institute and U.S. Census, Welch found that between 1986 - a year before PSA became accepted in medical circles - and 2005, an additional 1.3 million men have been diagnosed who would not have been if the screening test were not available. He estimated that 1,000 men need to be tested over 10 years to avoid one prostate cancer death.

"That means 999 aren't being helped," Welch said. "They get operated on and some of them have trouble because of their operation and the radiation from the treatment."

In fact, whether PSA testing saves lives has never been clearly proven. Doctors routinely recommend screening at age 50, but some suggest starting at age 40, particularly for men at high risk. In addition, last year a federal expert panel recommended not to screen men 75 and older.

Two large-scale clinical trials on the merits of the test conflict. After following men for a decade, an American study found that those who got annual PSA or rectal exams were not more likely to avoid death from prostate cancer than people who weren't tested. A European study found a benefit to screening - men tested every four years were 20 percent less likely to die of prostate cancers than those not tested.

Walsh, the author of "Dr. Patrick Walsh's Guide to Surviving Prostate Cancer," said the European study underscores that screening works. The decline in prostate cancer mortality - 33 percent in the past decade - can be attributed in part to good screening and early detection, he said.

He said that Welch's study does not take into account the many men in the study diagnosed as recently as 2005, and that it is too early to assume that these men have not benefited from screening. In addition, the paper sends the wrong message to African- American men, who are at higher risk of the disease and are often diagnosed at later stages, when the cancer cannot be successfully treated.

When prostate cancer is not treated early, it's more likely to spread to bone or require hormone therapy, which has even greater side effects, Walsh said.

"The final decision is what's better: Let a man find out he has cancer and let him decide if he wants to be treated and what treatment he wants? Or go back to the dark days - before PSA testing - where virtually every man diagnosed with prostate cancer died of the disease?" he said.

Dr. Michael J. Naslund, chief of urology and director of the Maryland Prostate Center at the University of Maryland Medical Center, said that while the PSA test is not perfect, that it has helped doctors find some cancers in time to save lives.

"I would argue that pre-PSA, prostate cancer was underdiagnosed," he said. "Now, since PSA, we find cancers when 75 to 80 percent of them are curable."

Simply because doctors are testing for prostate cancer, it doesn't mean they are always treating it, Naslund said. Most urologists take a measured approach when deciding whether to treat prostate cancer, talking their patient through all the options. In some cases, a wait-and-see method works well, particularly in older men whose quality of life would be diminished by aggressive treatment. For others, radiation and surgery are appropriate.

"I have a lot of men I'm watching that I'm not treating," Naslund said. "There's no question there are men who I have treated with prostate cancer, who didn't need it. But there are many more men who have been cured or would have had a miserable quality of life had we not found it and treated it."

Prostate cancer screening recommendations vary

* The American Cancer Society does not recommend routine testing for prostate cancer. Doctors should discuss early detection with their patients and offer PSA testing every year starting at age 50, the organization says.

* The U.S. Preventive Services Task Force, a government panel that issues federal recommendations on preventive medicine, does not endorse screening men 75 and older and says the evidence is inconclusive on whether the benefits outweigh the harm in younger men.

* The American Urological Association says doctors should offer the PSA test to men 40 and older, whether or not they show symptoms of prostate cancer.

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