Use of IsoPSA, a blood-based test that measures all prostate-specific antigen (PSA) isoforms, outperformed PSA in predicting the overall risk of prostate cancer and the risk of clinically significant cancer (Eur Urol 2017; doi.org/10.1016/j.eururo.2017.03.025). IsoPSA also reduced false-positive biopsies by 48% in a cohort of 261 men scheduled for prostate biopsy at five U.S.-based centers.
The authors were interested in exploring the clinical utility of IsoPSA, which is available for research use only in the U.S., because while PSA “is arguably the most successful blood-based cancer biomarker to date” it also is “tissue- but not cancer-specific,” leading to over-diagnosis and over-treatment of non-lethal cancers. At the same time, tests like Prostate Health Index or 4Kscore measure only a few known PSA isoforms.
The two clinical parameters of interest in the study were IsoPSA’s discriminatory power in distinguishing between prostate cancer with a Gleason score ≥6 and benign prostate conditions, and in distinguishing between high-grade (Gleason ≥7) and low-grade (Gleason 6) prostate cancer.
IsoPSA yielded an area under the receiver operating characteristic (AUROC) for distinguishing cancer versus a benign condition of 0.79 versus 0.61 for total PSA and AUROC of 0.81 versus 0.69 for total PSA in distinguishing high-grade cancer from low-grade cancer.
The authors collected but did not adjust the results for demographic parameters like age and race, but they speculate that doing so might improve IsoPSA’s performance.