The study, which followed 223 men whose early stage prostate cancer was left untreated, found that the tumor could become much more aggressive after 15 years - a follow-up period much longer than that done in most such studies.
As expected, the study found a high death rate in the earlier years for men with tumors that were fast-growing at the time of diagnosis, and a low death rate in those with less aggressive cancers.
But then came the flare-up. "The prostate cancer mortality rate increased from 15 per 1,000 person-years during the first 15 years to 44 per person-years beyond 15 years of follow-up," said a report in the June 9 issue of the Journal of the American Medical Association by researchers at Orebro University Hospital in Sweden.
Despite those dire numbers, the results do not necessarily cast doubt on the policy of watchful waiting for many patients with localized prostate cancer detected at an early stage, said Dr. Victor R. Grann, clinical professor of medicine and epidemiology at Columbia University and co-author of an accompanying editorial.
One reason is that the study included a relatively small number of patients, he said. Only 49 of the participants were still alive after 15 years.
But more importantly, the Swedish study began well before the use of advanced techniques such as magnetic resonance imaging to assess the malignancy of a tumor and, especially, before physicians began monitoring the status of prostate cancer by measuring blood levels of prostate-specific antigen (PSA), with increased PSA levels a warning sign of problems, Grann said. The patients were recruited between 1977 and 1984.
"PSA testing may have picked up the progression of the disease earlier," Grann said.
Watchful waiting might not be appropriate for younger patients, such as men in their 50s, he said. But those 70 and older could be spared the side effects of treatment, with the knowledge that a flare-up probably will not occur for at least a decade, Grann said.
The real implications of the Swedish study apply to current studies in which PSA screening is being used to monitor men with diagnosed prostate cancer, he said. The study indicates the need for following those patients for much longer than has been the rule, Grann said.
"The message of the study is that you can't tell anything about prostate cancer with a follow-up of five years," he said. "You need to follow patients for longer than five years, probably even longer than 10 years."
The need for such a long follow-up is a challenge to current practice, the editorial said.
"It is difficult to think in terms of conducting a randomized trial for screening with a horizon of 15 to 20 years, but perhaps that is exactly what will be necessary to really observe the impact of PSA screening on prostate cancer," it said.
By Ed Edelson