The study, “Effect of a Low-Intensity PSA-Based Screening Intervention on Prostate Cancer Mortality The CAP Randomized Clinical Trial,” was published in the Journal of the American Medical Association (JAMA).
Prostate cancer is the second most common cause of cancer death in men from the U.S. and U.K., behind lung cancer. U.S. estimates for 2018 predict about 165,000 new cases and over 29,000 deaths from prostate cancer.
The PSA test measures the blood levels of the PSA protein, which is often elevated in patients with prostate cancer. Although the test was initially approved in the U.S. to screen asymptomatic patients as well as to monitor disease progression, contradictory results from clinical trials led to different recommendations worldwide.
Ongoing debate focuses on the trade-off between reduced mortality rates in patients who undergo screening and the potential harm from over-detection and over-treatment.
Although detecting aggressive prostate cancer is crucial and needs to be done as early as possible, diagnosing harmless cancers severely impacts patients’ quality of life. These patients are at risk of infection following a biopsy, and may develop impotence and incontinence due to treatment.
To shed new light on this controversy, a research team from the universities of Bristol and Oxford conducted the CAP clinical trial (ISRCTN92187251). They compared the effect of a single PSA test to standard diagnosis with no PSA screening on patients’ mortality over a 10-year period. The research was funded by Cancer Research UK.
A total of 419,582 men (189,386 screened with the PSA test) ages 50 to 69 were studied at over 600 sites in the U.K., making CAP the largest trial ever to evaluate prostate cancer screening, the investigators said.
Results showed that PSA screening increased the detection of low-risk prostate cancers. A total of 8,054 cases (4.3%) were found in the screened group, while 7,853 cases (3.6%) occurred in the controls. However, the data demonstrated no difference in mortality.
Overall, the findings show the limitations of the PSA test as a unique strategy to screen for prostate cancer, and highlights the need to develop other tests to detect cancers that require treatment, the researchers said.
“Our large study has shed light on a highly debated issue,” Richard Martin, PhD, the study’s lead author, said in a press release.
“The results highlight the multitude of issues the PSA test raises — causing unnecessary anxiety and treatment by diagnosing prostate cancer in men who would never have been affected by it and failing to detect dangerous prostate cancers,” he said.
“Cancer Research UK is funding work that will allow us to follow the men for at least a further five years to see whether there is any longer-term benefit on reducing prostate cancer deaths,” Martin added.
Richard Roope, MD, senior clinical adviser and clinical lead for cancer at Cancer Research UK, said the trial “illustrates that we need to develop more accurate tools if we want to save men’s lives.”
“We’re funding research into faulty genes which make some men more likely to develop prostate cancer and studying how these genes could help doctors to identify patients who are more at risk,” Roope said.
“We do not recommend that the PSA test should be routinely offered to men without symptoms,” he added. “However, if a man is particularly worried about his risk of prostate cancer, he should have a full discussion about his risk with his GP.”