Novel PSA Assay Improves Prostate Cancer Diagnosis
The new test, IsoPSA, measures all PSA isoforms in serum and more accurately discriminates high-grade cancer from benign disease.
BOSTON—Researchers have reported findings from a study showing that a new way to measure serum PSA is more accurate than currently used assays in discriminating the presence or absence of prostate cancer (PCa) and high-grade from low-grade PCa.
The new test, called IsoPSA, is based on the fact that proteins produced by cancer cells have different 3D structures (isoforms) than the same proteins produced by normal cells, according to investigators. IsoPSA measures all of the different molecular isoforms in serum PSA and it does not matter which isoforms are present.
“It measures PSA in a way that's tightly linked to cancer biology because the disordered metabolism that occurs in cancer cells results in all these abnormal truncated or glycosylated forms of PSA that standard currently available assays don't measure,” lead investigator Eric A. Klein, MD, chair of Cleveland Clinic's Glickman Urological & Kidney Institute, told Renal & Urology News. Dr Klein, who presented study findings at the American Urological Association's 2017 annual meeting, noted that “there are dozens and maybe hundreds of those isoforms in the serum of patients with [prostate] cancer.”
In a prospective study of 261 men with PCa, he and his colleagues found that the specificity of the isoPSA assay in distinguishing high-grade PCa (Gleason 7 or higher) from benign disease (Gleason 6 or less) was 0.81. By comparison, total PSA assays had an AUC of 0.69.
The investigators compared isoPSA with the Prostate Cancer Prevention Trial (PCPT) risk calculator 2.0, which incorporates total PSA, free PSA, age, race, and digital rectal examination and prior biopsy findings. The PCTC calculator had an AUC of 0.67 for discriminating high-grade from benign disease.
“What we found is that isoPSA alone performs just as well as all of those variables,” Dr Klein said. Thus, isoPSA has the advantage of providing all of the relevant information for clinical decision making in a single simple blood test, he said.
In addition, study findings showed that the number of unnecessary prostate biopsies could have been reduced by 50%.
Dr Klein noted that isoPSA can be performed using standard chemistry platforms and does not require any specific equipment.
Currently available tests that measure PSA isoforms only measure 3 or 4 of them, and this is an important limitation. “The isoforms that exists in a patient at a given time change over time as the metabolism of the cancer changes,” Dr. Klein said. Thus, a currently available assay that identifies 4 isoforms in a man's serum may not find those isoforms the next time PSA is measured.
The IsoPSA test was developed by Cleveland Diagnostics, a company co-founded by Cleveland Clinic, in which it has financial interest. Dr Klein disclosed that he has no personal financial interest in the company. Dr Stovsky, who was part of Dr Klein's study team, is chief medical officer at Cleveland Diagnostics, in which he has financial interest.