A large 15-year study of men who had surgery for prostate cancer found only a small percentage died from cancer, adding to evidence that some men might be able to skip radical surgery to treat the often slow-growing tumors, U.S. researchers said on Monday.

The study of more than 12,600 men with prostate cancer who had their prostates removed found only 12 percent died from cancer 15 years later, even though some showed signs of having an aggressive type of cancer.

Many more men -- 38 percent -- died from causes other than cancer.

The study shows a remarkably low risk of dying of prostate cancer within 15 years for treated men, and supports the concept that men with slow-growing cancers may not need immediate treatment, said Dr. Peter Scardino of Memorial Sloan-Kettering Cancer Center in New York, whose study appears in the Journal of Clinical Oncology.

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

Doctors have routinely recommended prostate cancer screening for men over 50 using a blood test for prostate specific antigen, or PSA. The belief was that early diagnosis and aggressive treatment for any cancer is better than standing by and doing nothing.

But many prostate tumors are slow-growing and take years to cause harm. Some studies suggest many men are living with the side-effects of aggressive treatment with surgery and radiation for a cancer that may never have killed them.

Our results demonstrate the low lethality of these cancers after radical prostatectomy, Scardino and colleagues wrote.

They said in the United States, fewer than 2 percent of men with under age 65 opt to forgo prostate surgery in favor of regular testing for their cancers. And 73 percent of those ultimately have surgery within four years.

But a separate study in the journal Cancer by researchers at the Erasmus Medical Center in Rotterdam, the Netherlands, found that men with early stage prostate cancer who put off the surgery in favor of regular checkups were not overcome by anxiety.

The team sent questionnaires to 150 men to gauge their comfort levels about their treatment decision, as well as levels of depression and anxiety.

More than 80 percent of the 129 men who returned their surveys scored about the same as those in other surveys who decided to undergo treatment for early prostate cancer.

A large, international trial is under way comparing regular checkups versus radical treatment but that study will not be completed for several years.

Scardino said doctors now use a number of tools to predict which prostate cancers will spread and cause harm, including statistical models, PSA tests, magnetic resonance imaging scans and biopsies.

But more accurate ones are needed, he said, adding doctors would like to be able to do molecular or genetic testing to see if tumors have the capacity to spread.

If not, it would be safe to watch, Scardino said.

Medicine Cancer