A study of older men diagnosed with small, slow-growing prostate cancers carefully monitored by urologists found that less than a third eventually required treatment.

The finding suggests that someone with relatively unaggressive prostate cancer is unlikely to develop the metastatic form of the disease or die from it.

An analysis of long-term survival outcomes for 1,298 men with prostate tumors classified as low risk for aggressiveness showed that just one half of one percent of the men – followed for up to 18 years – died from their cancer, the researchers report in the Journal of Clinical Oncology.

Older men who have slow-growing prostate cancer are more likely to die from other causes, often heart disease — long before the prostate cancer grows to the point that it might shorten their lifespan, they write.

The men in the study were put under what is known as active surveillance, which included twice-yearly rectal exams and blood tests for prostate specific antigen or PSA, and annual prostate biopsies.

An increase in PSA can signal prostate cancer progression to higher-risk status.

"Our goal was to make absolutely sure we identified the people that we thought would be the absolute safest," said senior study author Dr. H. Ballentine Carter of Johns Hopkins Hospital in Baltimore.

In the United States, between 30 and 40 percent of men whose prostate cancer would qualify them for active surveillance take the option — a figure that has grown over time but still lags behind other countries, Carter says.

In a similar study appearing in the Journal of Urology, researchers said more than two-thirds of prostate cancers in the United States should qualify for active surveillance rather than immediate treatment such as surgery.

Such surveillance options should be offered to "an expanded population of well-informed men who may value preserving function above a small risk of disease progression," said Marc Dall'Era from the University of California, Davis, and Peter Carroll from the University of California, San Francisco, in an editorial accompanying that published study.

Carter voiced a similar viewpoint.

"It's extremely unlikely someone (meeting low-risk) criteria is going to be diagnosed with a cancer that is ultimately going to kill them," he said. For men diagnosed with very low-risk cancers, "the first thing you should be asking is not which treatment, but do I need treatment at all," he added.