The risk of prostate cancer diagnosis in men with an elevated PSA but low IsoPSA.

Abstract

292 Background: IsoPSA is a structure-based serum assay. Initial studies demonstrated that it outperformed total and percent-free PSA in detecting clinically significant prostate cancer (csPCa) (i.e., grade group (GG) ≥2) on biopsy. This led to an overall reduction in invasive testing and magnetic resonance imaging (MRI). We sought to compare the risk of csPCa in patients with an initially normal or high IsoPSA, thus assessing IsoPSA’s prospective predictive ability of csPCa. Methods: We performed a single-center retrospective review of patients (n=1578) who underwent IsoPSA testing from November 2016 to August 2022. Data was dichotomized into patients with normal (≤6) and high IsoPSA (>6). We collected the outcomes of any follow-up IsoPSA, prostate biopsy, MRI, and diagnosis of prostate cancer. In the case of multiple follow-up tests, the most recent one was recorded. Results: The median follow-up time of 1578 patients who underwent IsoPSA testing was 24 months (IQR 16-29). Among 541 patients with an initial normal IsoPSA, 60 (11.1%) had a subsequent high IsoPSA, 23 (4.3%) had csPCa on a subsequent biopsy, and 48 (8.9%) had suspicious lesions on MRI (PI-RADS 4-5). Among 1037 patients with an initial high IsoPSA, 366 (35.3%) had csPCa on a subsequent biopsy and 342 (33%) had suspicious lesions on MRI. The sensitivity of IsoPSA to predict csPCa was 94.1%, and its negative predictive value was 89.3%. Conclusions: With 24-month follow-up, 4.3% of patients with normal IsoPSA developed csPCa, suggesting that a low baseline IsoPSA provides durable information about the 2-year risk of csPCa.[Table: see text]