Men with prostate cancer who decide not to undergo surgery and instead opt to treat only the symptoms of their disease do just about as well as men who are operated on, at least in the initial six or seven years after diagnosis.

Neither strategy shields a man from serious side effects, such as impotence or urinary problems, although the spectrum of problems differs, depending on which therapy is chosen.

Those are the main conclusions of two studies, published in yesterday’s New England Journal of Medicine, that examined one of the most controversial issues in medicine - how to treat prostate cancer. While the research produced no clear winner between therapies, it adds important details to the complicated picture of risks and benefits each patient must confront.

“The decision will still be difficult,” said Lars Holmberg, a Swedish physician at Uppsala University, who helped lead the experiment. “But at least now we have a chance for better-informed guesses about a man’s future than we did before.”

Prostate cancer is one of the slowest-growing human cancers, and also one of the commonest. Small prostate tumors can be found in a majority of men who die in their eighties of other causes.

Some doctors oppose routine surgery in elderly men, and argue that a cure is unlikely, complications are common, and a patient is more likely to die of other causes before the tumor spreads and becomes fatal. Others argue that surgery is better, largely because doctors believe it extends life.

The debate was made more complicated in the last decade by the huge popularity of prostate specific antigen (PSA) testing, which measures the blood level of a protein made by growing prostate tissue, including tumors. PSA testing caused a spike of cancer diagnoses - and operations - in the early 1990s, especially in men who had no symptoms and were younger than the age at which prostate cancer had traditionally been found.

The Scandinavian study, which enrolled men from 1989 to 1999, straddled that period. Slightly more than half of patients had symptoms of prostate or urinary tract disease. In the rest, the cancer was found as the result of rectal examinations, PSA measurements and other tests.

In the experiment, nearly 700 Scandinavian men with prostate cancer were randomly assigned to either undergo potentially curative surgery or to use “watchful waiting” as the main approach to their disease.

Some of the men in the watchful-waiting group had surgery if they developed problems urinating. Many also received hormone or radiation treatments to shrink the size of their tumors (as did some of the surgery patients). None of those treatments was intended to cure them, however.

After about six years, 62 people in the watchful-waiting group had died, compared with 53 of those assigned to undergo an operation called a radical prostatectomy. Statistically, this outcome was a draw.

Men getting surgery, however, had only half the risk of dying of prostate cancer. This showed that radical prostatectomy appears to be curative in a substantial number of cases.

Furthermore, the cancer had spread to distant organs in only half as many men in the surgery group as in the watchful-waiting group. Because the average patient lives only two years once the disease gets to that stage, that observation suggests the surgery group may ultimately survive longer.

In the second study, the Swedish researchers asked the men about the complications of their disease and how much the problems bothered them.

Problems with sexual function were more common in the surgery group (80 percent) than in the watchful-waiting group (45 percent), as were problems of urine leakage (49 percent compared with 21 percent). Difficulty urinating was more common in the watchful-waiting patients (44 percent compared with 28 percent). Most of the surgery patients did not get “nerve-sparing” operations, which appear to reduce the risk of those complications.

Overall, about 35 percent of men in both groups reported “low or moderate” psychological well-being, and about 40 percent in both reported “low or moderate” quality of life.

Gunnar Steineck, an oncologist and epidemiologist at the Karolinska Institute in Stockholm, said that previously, the assumption was that if a patient chose surgery, he “had to trade quality of life to win length of life. The results [of the study] do not support that.”

Overall, Steineck said, “I think doctors are going to be on much safer ground depicting the alternative [treatment] scenarios.”

There may be debate among American physicians “about what does it mean in the real world,” said Martin I. Resnick, a urologist at Case Western Reserve University, and president-elect of the American Urological Association.

The average age of men in the Scandinavian study was 65. In the United States, the average age of men diagnosed with prostate cancer has been falling steadily and is now about 60. Furthermore, most cases are found through PSA testing and before the patients have any symptoms.

“It is not uncommon to find men in their early fifties who have prostate cancer, while that was highly unusual a decade ago,” he said.

How watchful waiting performs in that group is unknown, but a clinical trial is underway in Veterans Affairs hospitals here trying to answer the question.