In 2012, the U.S. Preventive Services Task Force concluded that prostate cancer screening provides “very small potential benefit and significant potential harms” and issued guidelines recommending against it. A new study by experts at Fred Hutchinson Cancer Research Center, published today in the journal Cancer, explores the impact that stopping prostate-specific antigen (PSA) screening would have on American men.
The researchers used statistical models to predict prostate cancer incidence rates and related deaths from 2013 to 2025. Their findings indicated that discontinuing PSA screening altogether would result in a 13 to 20 percent increase in prostate cancer mortality (an additional 36,000 to 57,000 deaths in the U.S.) compared with continuing PSA screening during this period.
There are many different ways to use the PSA test for screening, however.
“We feel more nuanced guidelines are more appropriate,” said senior co-author Dr. Ruth Etzioni, a biostatistician in the Public Health Sciences Division at Fred Hutch. The research showed that stopping screening at age 70 (age-restricted screening) is a better option that would reduce the number of men who receive unnecessary treatment while preventing most of the additional deaths that would come from discontinued screening.
The problem of overdiagnosis
According to the National Cancer Institute, most prostate cancers diagnosed in the United States are found through screening rather than a patient reporting disease symptoms. Unfortunately, PSA screening is known to lead to large numbers of overdiagnosed cases – situations in which the cancer that is found would not cause symptoms or death within a man’s natural lifetime.
Treating overdiagnosed cancers tips off a domino effect of harms, said Fred Hutch biostatistician Roman Gulati, the lead author of the study.
“Overdiagnosis causes anxiety for patients and families, imposes an unnecessary economic burden on individuals and misuses health care resources,” he said.
In addition, surgery and radiation deliver a high risk for erectile, urinary and bowel dysfunction. “Treating a cancer that is not destined to grow or present problems cannot improve quality of life for an individual,” Gulati said.
Discontinuing screening altogether would clearly eliminate 100 percent of all overdiagnosed cases. But stopping screening would also more than double the number of prostate cancers that had already advanced, or metastasized, by the time they were discovered.
“Intensely and aggressively screening would be associated with more lifesaving [than discontinuing all screening],” said Gulati, “but more men would also be overdiagnosed. In this study, we also consider the middle ground, which provides a much more favorable tradeoff.”
The risk for prostate cancer metastasis depends on age, time since disease onset, and markers of aggressiveness such as tumor stage and grade. The researchers noted that most prostate cancers are found in older men who show low-risk characteristics, and the Prostate Cancer Foundation confirms that more than 65 percent of prostate cancers are found in men older than 65. However, older men are also much more likely to be overdiagnosed.
In the new study, the researchers used two independently designed models to examine the effects of continued, age-restricted and discontinued PSA screening from 2013 through 2025. The models synthesized data to represent prostate cancer progression, detection, treatment and survival. The models used in the study were developed at the University of Michigan and Fred Hutch to investigate national prostate cancer trends.
The models predicted that mortality rates will rise with both age-restricted and discontinued PSA screening, but that additional deaths will increase significantly more slowly under age-restricted versus discontinued screening (5 to 8 percent instead of 13 to 20 percent). PSA screening limited to men under age 70 could prevent a majority of the deaths that are avoided with current screening while dramatically reducing the number of overdiagnoses.
“These tradeoffs underscore the potential for smarter ways of using the PSA test,” Gulati said. “Restricting PSA testing to men under 70 years of age is just one such approach. More generally, rather than discontinuing screening completely, our results support developing more efficient ways to use the PSA test to screen for prostate cancer.”
Lifestyle factors also play an important role
Despite the Task Force guidelines, said Etzioni, the test is still available and being performed in healthy men. Many organizations, such as the American Cancer Society, the American Urological Association and the American College of Physicians recommend shared decision making about PSA screening for men under age 70 who can reasonably expect to live at least 10 years.
“Patients need to know that screening has potential benefits as well as potential harms,” said Etzioni, “and it has to be considered in the context of a man’s lifestyle and any other conditions that may affect his health.”
While screening has its place, Etzioni said boosting overall health through lifestyle factors such as not smoking, eating a healthy, balanced diet and getting enough exercise can go a long way toward extending a man's life expectancy. For example, when it comes to prostate cancer, research at Fred Hutch has found that obesity and long-term, heavy smoking significantly increase the risk of an aggressive form of the disease. Hutch researchers also have found that moderate coffee and red wine consumption and eating a diet rich in cruciferous vegetables may help prevent prostate cancer.
Regardless of whether PSA testing is used for screening, the test remains an important tool for post-treatment monitoring of patients whose prostate cancer has been confirmed by a biopsy.
Researchers from the University of Michigan, University of Washington, National Cancer Institute and University of California, San Francisco, collaborated on the study, which was funded by the NCI’s Cancer Intervention and Surveillance Modeling Network.
Solid tumors, such as those of the prostate, are the focus of Solid Tumor Translational Research, a network comprised of Fred Hutchinson Cancer Research Center, UW Medicine and Seattle Cancer Care Alliance. STTR is bridging laboratory sciences and patient care to provide the most precise treatment options for patients with solid tumor cancers.
Joely Johnson Mork is a Seattle-based freelance health and science writer/editor whose work has appeared in numerous consumer health books, as well as in Prevention and TIME. Her personal essays have been heard on NPR. Mork has a master’s degree in community health education and is a certified yoga instructor.