Low Baseline IsoPSA Index is Associated With a Prolonged Low Risk of Clinically Significant Prostate Cancer Diagnosis...

To compare the rate of diagnosing clinically significant prostate cancer (csPCa) in men with elevated prostate-specific antigen (PSA) stratified by baseline IsoPSA Index, thus assessing IsoPSA's intermediate-term predictive ability for csPCa.

Single-center retrospective review of consecutive patients (n = 1578) who underwent IsoPSA testing from November 2016-August 2022. Data dichotomized into patients with low (≤6) and high IsoPSA Indices (>6). Most recent subsequent IsoPSA and PSA tests, prostate biopsy, and magnetic resonance imaging (MRI) collected. Time-to-event Kaplan-Meier estimates generated for the risk of csPCa stratified by baseline IsoPSA Index.

Among 541 patients with initial low IsoPSA Indices (≤6), 23 (4.3%) were diagnosed with csPCa on a subsequent biopsy. Also, among these 541 patients, 204 had an MRI, of which 48/204 (23.5%) showed suspicious lesions (PIRADS ≥4). Among 1037 patients with initial high IsoPSA Indices, 366 (35.3%) were diagnosed with csPCa on a subsequent biopsy. Also, among these 1037 patients, 712 had an MRI, of which 342/712 (48.0%) showed suspicious lesions (PIRADS ≥4). After 12, 24, and 30 months, respectively, the risk of developing csPCa was 0.4% (95% CI 0.1%-1.6%), 2.5% (1.4%-4.4%), and 6.3% (4%-9.6%) in patients with low IsoPSA Indices, compared to 5.9% (4.6%-7.6%), 31.7% (28.3%-35.4%), and 49.5% (45.3%-53.9%) in patients with high IsoPSA Indices. Limitations include the retrospective review of prospectively collected data and unknown true csPCa rates as not all patients were biopsied.

The risk of developing csPCa was smaller in patients with initial low vs high IsoPSA Indices over the ensuing 30 months, which supports using IsoPSA to safely avoid follow-up testing.