Researchers continue to try to improve upon the blood test used to screen for prostate cancer — the prostate-specific antigen (PSA) test. A new test claims to help physicians get more accuracy and avoid unnecessary biopsies.
The PSA test measures a protein that comes from cancerous and noncancerous tissue in the prostate gland. While the test detects PSA, it doesn’t offer more information about the condition of the prostate and other factors that can help doctors prevent overtreating the disease. As a result, many patients with high PSA levels have gone through unnecessary diagnostic procedures and treatments in the past.
Introducing the IsoPSA
A new blood test, the IsoPSA, showed promise in trials to more accurately diagnose prostate cancer. It can help physicians discern if they should noninvasively monitor the disease or go forward with cancer treatment. Details on the test were presented at the recent American Urological Association (AUA) conference in San Francisco.
According to study authors, the IsoPSA can result in about 40 percent fewer biopsies.
In fact, 45.1 percent biopsies would have been avoided according to the preliminary study. In a second validation study, the researchers found up to 47 percent of biopsies could have been thwarted.
The authors say that the new test may reduce overdetection and overtreatment of nonlethal prostate cancer because it can discern high-grade cancers from low-grade benign forms of the disease.
Dr. Eric Klein, chair of Cleveland Clinic’s Glickman Urological Kidney Institute, led the multicenter validation trial. His team assessed the data with a new cohort that included cutoff parameters taken from a preliminary study.
“To be clinically useful, a biomarker must be both tissue-specific and cancer-specific. While PSA is prostate-specific, it is not specific for prostate cancer, leading to diagnostic inaccuracy and too many unneeded biopsies,” Klein said.
Klein said the new IsoPSA test looks at biomarkers specific to both cancer and tissue.
“This validation study shows that it can more accurately detect high-grade cancer and reduce the rate of unneeded biopsies in patients at low risk of this disease,” he said.
Problems with the PSA
Richard J. Ablin, PhD, DSc, a professor at the University of Arizona, discovered the PSA in 1970 when he was trying to find out which antigen was specific to prostate cancer. But PSA was found in all prostates, though he believed elevated PSA could be helpful to predict prostate cancer recurrence.
When the Food and Drug Administration approved the test in 1994 as a cancer detection method, Ablin cautioned against using it as a measure of preventive screening.
The test isn’t always accurate because PSA levels can fluctuate and high levels can be attributed to ailments other than cancer. Men with high readings have sometimes sought treatment upon finding out they had high PSA levels. This treatment can lead to other side effects including impotence and incontinence. Plus, the test has been thought to only find the low-grade cancers instead of the most aggressive types.
Some medical trials have found that the PSA test didn’t result in better survival rates.
Other studies have stated that anywhere from 23 percent to 42 percent of men who have prostate cancer have tumors that wouldn’t produce symptoms during their lifetimes. In other words, the PSA test would drive men to treat a disease that would never impact them.
Andrew Vickers, PhD, attending research methodologist at Memorial Sloan Kettering Cancer Center in New York City, said that the IsoPSA is similar to other PSA tests that identify biomarkers of the disease more specifically. His team developed one of them — the 4Kscore.
He explained that when a man had a PSA test that came back elevated in the past, the doctor will typically conduct the test again in about six weeks. If the levels didn’t go down, he was then referred to a urologist. The urologist would look at other reasons for the elevated PSA. Then they would probably conduct a biopsy.
“The problem with that is most men with elevated PSA don’t have a high-grade cancer, they have a low-grade cancer,” Vickers told Healthline. PSA readings and biopsies can lead to over diagnosis, and in many cases overtreatment.
Treating the disease didn’t seem to reduce deaths from it.
New PSA test options
PSA measures different molecules that appeared in the blood in different ways, Vickers said. Tests that could better identify specific biomarkers linked to aggressive cancer were a big development when they came on the market. They offered more accuracy so men would know if they needed biopsies and treatment.
Nowadays, the more specific tests, such as the 4Kscore, are used after multiple elevated PSA screenings to see if high-grade cancers exist or if the cancer should simply be monitored. With more accurate testing, physicians are hoping to conduct biopsies only when needed. This is why these more specific tests such as the IsoPSA are so helpful — they can make it so biopsies are not conducted needlessly.
Having more accurate tests such as the 4Kscore and others already on the market are a “game-changer,” Vickers said. “These tests have very dramatic implications for how we understand PSA in general.”
“The IsoPSA adds to the range of tests we have available,” Vickers said. “It’s comparable to other tests.”
Dr. Anthony D’Amico, a radiation oncologist at the Dana-Farber Cancer Institute in Boston, told Healthline that the results of the IsoPSA are promising and worthy of further study.
He questioned what the performance characteristics of the test were in men at high risk for being diagnosed with the disease (such as African American men, who often have a more aggressive disease and a higher mortality rate), compared to men with family history who have a high risk of being diagnosed but may not have a clinically significant disease.
While the test warrants further study in high-risk and average-risk populations before it could be used for all men, it could be considered in certain conditions. The test could be considered for someone with an elevated and rising PSA who has undergone at least two sets of biopsies and has no evidence of cancer to see if more testing is needed, D’Amico said.
But Ablin said IsoPSA doesn’t solve all the issues with the PSA as a tool for prostate cancer detection. It offers a different calculation based on the PSA test — a test that is “flawed” as far as being able to accurately detect prostate cancer.
“A biopsy is the ultimate diagnostic test,” he said, noting that there is more attention on using magnetic resonance imaging (MRI) to detect prostate cancer.
While some see the IsoPSA as a promising step, Ablin told Healthline there isn’t much to get excited about.
“This test will not change the way prostate cancer is diagnosed,” Ablin added.