Study Questions Value of Prostate Cancer Screening
Widespread screening for prostate cancer over the past 3 decades using the prostate-specific antigen (PSA) test has led to a flood of men being diagnosed with and treated for prostate cancer that never would have harmed them, according to a new study. The jump in diagnoses was most pronounced among younger men, with rates more than tripling for men aged 50 to 59 and increasing seven-fold for those aged 50 and younger. The study was published online August 31 in the Journal of the National Cancer Institute (JNCI).
That PSA screening has resulted in significant prostate cancer “overdiagnosis,” as it is often called, is not new. Results from two clinical trials published earlier this year pointed to an identical conclusion. The new study, however, places the extent of the problem in stark context, estimating that in the 30 years since PSA testing was introduced, approximately 1.3 million more men have been diagnosed with prostate cancer than otherwise would have in the absence of such screening, and concluding that very few men’s lives have been saved as a result.
The findings, said study co-author Dr. H. Gilbert Welch of Dartmouth Medical School, “show that there’s been a pronounced population effect” associated with PSA testing; that it’s “not just a theoretical problem seen in a clinical trial.”
To conduct the study, Dr. Welch and his co-author, Dr. Peter C. Albertsen of the University of Connecticut School of Medicine, relied on NCI’s Surveillance, Epidemiology, and End Results (SEER) program and the U.S. Census to get data on age-specific incidence of prostate cancer and patients’ initial treatment following diagnosis from 1986 to 2005.
The base year, 1986, was chosen because it was the year before an influential study on PSA screening appeared in the New England Journal of Medicine. Prostate cancer incidence increased 10 percent the following year, “a magnitude of increase never before observed for prostate cancer in the SEER program and a magnitude that strongly suggests the onset of screening,” the authors explained.
Among the estimated 1.3 million excess prostate cancer diagnoses, slightly more than 1 million men received definitive treatment, such as surgery, hormone therapy, or radiation therapy. “But even using the most optimistic assumption about benefit, the vast majority of these additional 1 million men did not benefit from early detection,” the authors wrote.
That point, said Dr. Marc Garnick from Beth Israel Deaconess Medical Center in Boston, shows that the term “overdiagnosis” may incorrectly describe this problem. “I think it’s perfectly reasonable to diagnose patients” based on PSA screening, he said. “The problem is that many men have been over treated.”
Dr. Peter Carroll, chair of the University of California, San Francisco’s (UCSF) Department of Urology, agreed. “When first diagnosed, patients view prostate cancer like lung and pancreatic cancer. They don’t differentiate it from much more lethal forms of disease,” he said. “We have to get that out there, in patients’ and physicians’ minds, that prostate cancer can be a manageable disease” without immediate treatment.
At Beth Israel and UCSF, a growing population of men who undergo PSA testing and are considered to be at low risk for progression of the disease—based on factors such as age, degree of cancer involvement on the biopsy, Gleason score (an indication of the tumor’s potential aggressiveness), and other factors—are choosing active surveillance, where they carefully watch for symptoms and come in for periodic biopsies to monitor their disease.
But even active surveillance has significant implications, Dr. Welch countered, from the regular biopsies to the social impact of being considered a person with cancer. Education and communication are needed before the first PSA test is conducted, he said.
“Those who undergo PSA screening…should be informed patients who accept the harms and want to get the relatively small benefit, and accept all of the side effects that can occur along the way,” he said.
At the same time, it should be noted that prostate cancer mortality has fallen 40 percent since 1993, most likely due in some part to PSA screening. An NCI-supported modeling study published last year suggested that PSA screening was responsible for as much as 70 percent of the decrease because testing shifted the stage at which the disease was diagnosed. And one of the two recently published prostate cancer screening trials, conducted in Europe, suggested that screening with PSA had a modest effect on prostate cancer mortality. The same trial, however, estimated that more than 1,400 men would have to be screened, and nearly 50 treated, to prevent 1 prostate cancer death.
In an editorial that accompanied the JNCI study by Drs. Welch and Albertsen, American Cancer Society Chief Medical Officer Dr. Otis Brawley took a grim view of widespread PSA screening. “Results from this article and recent results from prostate cancer screening and prevention trials demand reflection about what we as a society have done and are doing,” he wrote.