Roughly one-third of older men diagnosed with prostate cancer with a routine blood test are "overdiagnosed" with the disease, according to a Fred Hutchinson study conducted by Dr. Ruth Etzioni.
The study quantifies for the first time a concern that the medical community has had for years: that a blood test called PSA screening, in use for the past decade, diagnoses more men with prostate cancer than may ever experience its symptoms.
Etzioni found that among U.S. men age 60 to 84 with prostate cancers detected by the PSA screening, about 29 percent of whites and 44 percent of blacks would otherwise not have been diagnosed by clinical exam or developed symptoms during their lifetimes.
"What we can say is that our results do raise caution for older men who undergo testing, since considerable morbidity (unhealthiness) can be associated with treatment for prostate cancer," Etzioni said.
"These findings are an important step toward calculation of the cost-effectiveness of PSA screening," she said.
Etzioni cautioned, however, that establishment of guidelines for testing awaits results of randomized clinical trials to evaluate PSA screening's effectiveness at reducing mortality.
The PSA test, originally developed to monitor disease progression, has been widely used for early cancer detection since its introduction in the mid-1980s, but there has been no rigorous assessment of its effectiveness for such screening. The procedure measures the level of a protein-prostate-specific antigen-produced by the prostate gland which, when elevated, can signal the presence of cancer.
As use of the test became prevalent, prostate-cancer incidence increased sharply and had more than doubled by 1992 before going back down.
This apparent surge in incidence prompted concern over prostate-cancer overdiagnosis, which might lead to unnecessary treatment for indolent tumors.