The study finds that PSA blood tests every four years seem to cut the risk of death from prostate cancer. But it also finds that screening makes no difference in overall mortality rates because most men die of other causes — not their prostate tumours.
The results underscore a frustrating truth about this disease: most prostate cancers grow too slowly to threaten a man's life and there is no good way to tell which ones will. Finding cancer often leads to treatments that can cause impotence, incontinence and other problems. The PSA test also is just a measure of inflammation, which can be due to many things besides cancer.
"A man needs to make a choice for himself, realizing the benefits exist in theory, but the harms have been shown in every study that we've ever done in prostate cancer," said Dr. Otis Brawley, chief medical officer of the American Cancer Society. "If there is an overall mortality benefit from prostate screening it is very, very small."
He had no role in the study, which was published in Thursday's New England Journal of Medicine.
In October, a government-appointed panel of experts, the U.S. Preventive Services Task Force, recommended against screening with PSA tests. Only two big studies have looked at this — a U.S. one that found annual screening did not cut prostate cancer death risk and a European one that found screening every four years did. (In Europe, prostate screening is less common and is done at wider intervals than in the United States.)
The new research is longer follow-up from the European study: 11-year results on 162,000 men ages 55 to 69. Researchers found that 1,055 men would need to be offered screening and 37 cancers would need to be detected to prevent a single death from prostate cancer. Overall death rates did not differ between the group offered screening and the group not offered it.
About half of the cancers that were detected did not need to be treated, researchers estimate.
The study was led by Dr. Fritz Schroder of Erasmus University Medical Center in the Netherlands. Several authors hold patents or get fees from PSA tests.
Men who choose to be screened should be prepared for a tough discussion of whether to have a biopsy or to treat any cancer that is found, said Dr. Christopher Logothetis, prostate cancer research chief at the University of Texas MD Anderson Cancer Center in Houston.
Prostate cancer "is only one of the causes of death, and it is not the main cause of death in these patients," he said.
Others believe the study supports the value of PSA tests and think the benefit will become clearer with even longer follow-up.
"Urologists are very passionate about it because we see all the bad cases," said Dr. Stephen Freedland, a Duke University urologist who has consulted for a few makers of prostate cancer drugs.
"What we need to do is separate screening from treatment. Not everyone diagnosed needs to be treated. But the best way of knowing who to treat is getting a sense of how bad the cancer is," he said. Annual tests may be too often, "but I don't think the solution to that is to give up all screening."
Prostate study: http://www.nejm.org/doi/full/10.1056/NEJMoa1113135
Task force advice: http://www.uspreventiveservicestaskforce.org
Cancer society advice: http://tinyurl.com/257mnge
PSA decision guide: http://bit.ly/cXq1QE
Marilynn Marchione can be followed at http://twitter.com/MMarchioneAPSuggest a correction