Low-risk prostate cancer is the form of the disease deemed to be non-aggressive and slow-growing. Instead of aggressively treating the cancer with surgery or radiation, doctors typically advise men to go on a regimen of "active surveillance."
As part of that regimen, patients have their levels of PSA, or prostate-specific antigen, regularly monitored and have periodic biopsies of the prostate gland to see if the status of their cancer has changed over time.
"And this poses, as best as we can tell, very little threat to life of the vast majority of men who have it," said the study's principal investigator Dr. Neil Fleshner, head of urology at Toronto's University Health Network.
"And if it does, it may be 20 or 25 years down the road," he said, noting that about half to two-thirds of men with prostate cancer in western countries are diagnosed with this form of the disease.
To conduct the three-year clinical trial, researchers enrolled 302 men with low-risk prostate cancer, aged 48 to 82. Half received the drug dutasteride (brand name Avodart), while the other half got a dummy pill. The men also had biopsies at 18 and 36 months.
The study showed a significant delay in disease progression in the men treated with the drug, which along with Proscar (finasteride) belongs to a class of medications known as 5a-reductase inhibitors. Among those who received the drug, 38 per cent saw their disease progress, compared to 48 per cent of those in the placebo group.
As well, the men treated with the drug were less likely to have cancer detected in their final biopsy of the study — 36 per cent compared with 23 per cent.
"I think that's a real important finding that should be highlighted," said Fleshner. "So that's a 13 per cent difference in men's cancers all sort of vanishing."
He said that when men see their biopsies coming back looking normal, they're more likely to stay on the active surveillance program — instead of demanding surgery or radiation, based on the fear that when dealing with cancer, any treatment is better than none.
"What we found was the men who were randomly allocated to the dutasteride drug were less likely to say, 'I'm out. I can't tolerate the stress of being on surveillance any more,'" Fleshner said. "And they were also less likely to have a worse pathology report as their subsequent biopsies went forward."
Fleshner said the study, published online Monday in The Lancet, shows that active surveillance while taking the drug is a safe, effective option for men whose risk of dying from the disease is considered minimal.
"This is very good news for men with low-risk disease because aggressive treatment can have a major impact on their quality of life, with risks of impotence and incontinence," he said.
Toronto political strategist John Laschinger, 69, was diagnosed with prostate cancer in late 2006 and put on active surveillance. When the study results pointed to a benefit from dutasteride, Fleshner suggested his patient start taking the drug.
"So I've been on the drug for the last year and a half and my PSA is now dropped by two-thirds," he said Monday. His biopsies show his prostate is "clean," with no cancer cells being detected.
"When you go and you get the results back and the thing is under control, it does give you a certain level of comfort ... And this drug looks like it reduces the PSA, reduces the rate of growth of cancer development in the prostate — and it's a no-brainer."
Urologist Dr. Martin Gleave, director of the Vancouver Prostate Centre, said the study is important because it illustrates an approach to treating men with low-risk cancer.
"So on the one hand it helps to deal with the psychological burden of active surveillance, but on top of it there is evidence that it can delay progression of the low-risk type of cancer and hence reduce the risk of subsequent need for surgery or radiation down the road."
Fleshner said the study is the first to show that a 5a-reductase inhibitor, which works by suppressing a male sex hormone, reduces the need for aggressive treatment in low-risk disease.
The drug did cause side-effects in a small percentage of men in the study, including difficulty with sexual desire or erections as well as breast tenderness or enlargement. Stopping the drug reverses these side-effects.
"I think it tells us that by using these drugs we can keep men free of unnecessary treatment for longer periods of time," Fleshner said. "And I think ... hopefully this will improve the acceptance and make more men likely to choose this option."
The Canadian Cancer Society estimates 25,500 new cases of prostate cancer will be diagnosed this year and about 4,100 men will die from the disease.