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Doctors caring for patients with early stage prostate cancer may do better to watch and wait to see if tumors develop rather than engage in aggressive treatment that may do no good, scientists said on Tuesday.

A study in the Journal of the American Medical Association found the risk of dying from prostate cancer in the 10 years after diagnosis fell by more than 60 percent in patients diagnosed between 1992 and 2002 compared with patients diagnosed in the 1970s and 1980s.

But doctors only manage 10 percent of cases conservatively by watching closely and delaying treatment until symptoms demand it.

When diagnosed, prostate cancer is contained within the prostate in approximately 85 percent of cases, and standard treatment options usually include surgery, radiation or conservative management, the researchers wrote.

Prostate cancer is the second most common cancer in men worldwide after lung cancer, killing 254,000 men each year.

But there are fears that in some countries such as the United States, it may now be being overdiagnosed and treated more aggressively than necessary.

All current treatments -- surgery, radiation or hormone therapy -- can cause harm and lead to impotence and incontinence in about a third of patients. The authors of Tuesday's report said with that in mind, doctors and patients should reconsider the watch and wait option.

A study published in August showed routine screening for prostate cancer has led to more than 1 million men in the United States being diagnosed with tumors who might otherwise have suffered no ill effects from them.

For Tuesday's study, Grace Lu-Yao and colleagues at the Cancer Institute of New Jersey studied 14,500 men 65 or older when they were diagnosed -- between 1992 and 2002 -- with early stage prostate cancer and who were cared for without surgery or radiation for 6 months after diagnosis.

They found that after 10 years, 6 percent had died from prostate cancer, far fewer than in results of previous studies dating from 1949 to 1992, when between 15 and 23 percent died within 10 years of being diagnosed.

Patients tend to over-estimate the effects of treatment. They tend to see cancer as a life-threatening disease and think treatment will save their lives, Lu-Yao, a cancer epidemiologist, said in a telephone interview.

But prostate cancer is sometimes different from other cancers, and with these early screenings, for a lot of people it really won't cause a problem during their lifetime.

Lu-Yao said the improvement in diagnosis and survival rates could relate to the introduction in 1986 of a widely used blood test that looks for a prostate specific antigen, or PSA.

PSA testing can pick up disease 6 to 13 years before it may otherwise be found, and patients identified in such tests would be expected to live between 6 and 13 years longer because of this lead time, the authors said.

Doctors in the U.S. have routinely recommended PSA screening in men over 50 based on the assumption that early diagnosis and treatment is better than standing by and doing nothing.