Marilynn Marchione, AP Medical Writer

A new study suggests a way to help men with early, low-risk prostate cancer avoid being overtreated for a disease that in most cases will never threaten their lives. It found that a drug can slow the growth of these tumors in men who opt to be monitored instead of having treatment right away.

This is the first time that a drug for treating enlarged prostates also has been shown to help treat prostate cancer in a rigorous study. It may persuade more men to choose active surveillance, or "watchful waiting," instead of rushing to have treatments that can leave them with urinary or sexual problems, doctors say.

However, the results also show that most of these men do very well with no treatment at all.

"We’re identifying men who are not likely to need even a pill," said Dr. Maha Hussain, a University of Michigan cancer specialist. But Americans fear cancer so much that they want some kind of treatment and underestimate the financial and medical risks of treating low-risk cases, she added.

She is program chair of a cancer conference in Florida where the study will be presented later this week. Results were released Tuesday in a telephone news conference sponsored by the American Society for Clinical Oncology.

Roughly half of the 218,000 men diagnosed each year in the United States with prostate cancer have low-risk disease — PSA blood levels under 10 and low tumor aggressiveness scores.

"The American view of cancer" is that it’s always best to treat, so about 80 percent of these men choose to have that right away, said Dr. Otis Brawley, a prostate cancer expert who is chief medical officer of the American Cancer Society.

In Europe, though, most choose watchful waiting — close monitoring and treatment only if the cancer progresses or causes pain or other problems.

Doctors know that drugs that shrink the prostate — GlaxoSmithKline PLC’s Avodart and Merck & Co.’s Proscar — can help prevent prostate cancer. But federal health advisers recently recommended against taking them for this purpose because of potential risks.

The new study tested Avodart "not to prevent cancer, but to prevent the progression" of it in men who already have the disease, which may be a much better use of such drugs, said the study’s leader, Dr. Neil Fleshner of University Health Network and Princess Margaret Hospital in Toronto.

"We know the vast majority of these men are not destined to die from that cancer," and wanted to see if Avodart could make "watchful waiting" safer, Fleshner said.

The study enrolled about 300 men in the United States and Canada with low-risk cancer that was confirmed by a biopsy. They were given daily Avodart or dummy pills and new biopsies 1½ and three years later.

Prostate cancer got worse in 38 percent of men taking Avodart and 49 percent of those on dummy pills. Final biopsies showed no signs of cancer in 36 percent of men on Avodart versus 23 percent of those on dummy pills. Doctors say this last result shows how tiny many of these cancers were to start with, that they couldn’t even be found when new biopsies were done.

Doctors don’t think Avodart can cure cancers, but it seems to suppress it, said Dr. Howard Sandler, a prostate cancer specialist at Cedars-Sinai Medical Center in Los Angeles. He had no role in the study but is involved with the cancer conference.

Researchers gave no details on Avodart’s side effects, but said no new ones appeared in the study. Avodart and Proscar are known to cause sexual problems for some men, but many men over 50 have this anyway and only about 5 percent more do when taking these drugs, said Brawley, who helped test Avodart for cancer prevention.

The new study was sponsored by Avodart’s maker, GlaxoSmithKline. Avodart and Proscar cost about $4 a pill; generic versions of Proscar are available for about $2. Proscar is similar to Avodart but has not been tested for treating early cancer as this study did.

Sandler said Avodart might relieve some men’s anxiety about monitoring their disease and may make them more comfortable not having immediate treatment.

"If it was me, I’d choose active surveillance," he said. Avodart "has the potential to be an important help."