It's Prostate Cancer -- Or Is It?
Study says common screening method leading to over-diagnosis
TUESDAY, July 2, 2002 (HealthDayNews) -- A large number of men who are given the scary news that they have prostate cancer are being rattled -- and perhaps treated -- unnecessarily, a new study suggests.
The diagnosis for those men is based on detection of high levels of prostate-specific antigen (PSA), a molecule associated with the malignancy. The computer study concludes that many of them -- 29 percent of whites, 44 percent of blacks -- would be better off not knowing that diagnosis because they would die of other causes before the cancer did any damage.
PSA testing was approved by the U.S. Food and Drug Administration in 1986 as a way to monitor treatment of prostate cancer. Starting in 1988, it has been used more and more for detection, even though there is mixed evidence to say it works well for that purpose. Diagnoses of prostate cancer rose sharply after the PSA test went into widespread use.
The study, appearing in tomorrow's issue of the Journal of the National Cancer Institute, says a lot of those diagnoses are doing more harm than good because they lead to men getting treatment they don't need.
"Considerable morbidity can be associated with treatment for the disease," says study leader Ruth Etzioni, a biostatistician at the Fred Hutchinson Cancer Research Center in Seattle.
The importance of that conclusion is illustrated by some numbers. The American Cancer Society estimates that 189,000 cases of prostate cancer will be diagnosed this year. There will be 30,200 deaths, making prostate cancer the second leading cause of cancer deaths in men.
Many of those diagnoses will be made on the basis of something other than the PSA test. To determine the effect of PSA testing, Etzioni and her colleagues created a computer model using government cancer registry data.
"The reason we used a computer model is that the real world is a very uncontrolled setting, with a lot of multiple factors that can affect prostate cancer incidence," Etzioni says. "The model allows us to understand one of those factors."
The model was based on a hypothetical group of men aged 60 to 84. The estimated percentages of over-diagnoses (higher for blacks than whites because they are more susceptible to the cancer, for unknown reasons) were based on two factors: Either the cancer would grow so slowly that it would not affect a young man, or an older man would die of other causes before the cancer caused a problem.
Unfortunately, the model provides no guidance for a man who is told his PSA level is high enough to require treatment, Etzioni says. Men with high PSA levels are more likely to be diagnosed with the disease, she says, but the PSA levels that indicate a real danger aren't known, she says.
"This has to be determined by molecular biology tools," Etzioni says. "A lot of work is going into developing clinical models."
This is "definitely not a trivial problem," says Grace Lu-Yao, director of HealthStat, a consulting group, who is co-author of an accompanying editorial. "This is especially so because the process of prostate-specific enzyme screening has not been proven to reduce cancer mortality."
The best advice Lu-Yao can offer a man told he has a dangerous PSA level is to "talk with your doctor and really understand what it means." Having surgery or other treatment for prostate cancer can cause physical problems, while not doing anything can cause major anxiety, she says. So, a talk with a doctor before having the PSA test seems advisable.
"For those who choose to discuss the option of screening with their health-care provider, the important possibility of over-diagnosis should not be overlooked," Lu-Yao says.
The American Cancer Society recommends a combination of PSA testing and a digital rectal examination for men of average risk annually starting at age 50, "with an explanation of the benefits and limitations" of the tests, says Dr. Durado Brooks, director of prostate cancer for the society.
"For high-risk men, which we define as African-Americans and those with a family history of the disease, we recommend the screening begin at age 45," Brooks says.
One limitation of the study is it does not include men under the age of 60, Brooks notes.
"It is also important to point out that it is not based on actual numbers of actual cases," he says. "But within its limitations, it offers interesting information."
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