For the first time, a study clearly shows that surgery for early prostate cancer can reduce the chance of dying from the disease, cutting the risk almost in half.

The question of whether to remove cancerous prostates in early-stage disease has been debated because the cancer typically grows slowly and strikes older men, who may die of other causes before it spreads.

Moreover, removal of the prostate a doughnut-shaped gland that surrounds the male urethra can cause serious side effects, including impotence and incontinence.

In the latest study, conducted on 695 men in Sweden, Finland and Norway, the risk of dying from prostate cancer fell from 9 percent to 5 percent during the six years after surgery.

However, deaths from all causes were similar between the men who got prostate surgery and those who did not. The researchers said it could have been a matter of chance that those who escaped cancer death were somewhat more likely to die of other things.

“We now have better evidence that radical prostatectomy diminishes your risk of prostate cancer recurrence. And so we have a possibility to alter the natural course of the disease by radical surgery,” said Dr. Lars Holmberg, lead author for the paper.

A companion study also published in today’s issue of the New England Journal of Medicine found no difference in quality of life between the groups, though it suggested a longer study might find such differences.

The cancer spread elsewhere in the body in 35 of the men whose prostates were removed immediately, compared to 54 in the “watchful waiting group,” Holmberg wrote.

But, although the total number of deaths was slightly lower among the treated group 53 to 62 it wasn’t a big enough difference to be statistically meaningful, wrote Holmberg, an epidemiologist at the regional cancer center at University Hospital in Uppsala, Sweden.

Dr. Patrick Walsh, director of urology at Johns Hopkins University, called Holmberg’s a landmark paper.

“It was surprising to see an effect from cancer deaths so early,” he said. “It’s certainly too early to see an overall effect on survival,” But, he said, he thinks such an effect is likely with longer follow-up.

It may be the first study for any cancer in which patients were assigned at random to get surgery or no treatment what doctors call “watchful waiting” or “expectant observation,” he said.

Walsh is an advocate of early surgery and developed a technique used to preserve the nerves that control the penis’s ability to become erect.

And, even if the death rate difference doesn’t grow, just reducing the number of deaths from prostate cancer is worth it, he said.