Can magnetic resonance imaging safely replace a confirmatory biopsy in patients on active surveillance for prostate cancer?

Abstract

331 Background: Active surveillance (AS) is recognized as the preferred management for patients with low-risk prostate cancer, and many with favorable intermediate risk tumors as well. AS has been increasing in utilization both within the Veterans Affairs (VA) Healthcare System and nationally in the U.S. However, the limited data evaluating the quality of AS protocols suggests wide variability. One area of controversy is whether magnetic resonance imaging (MRI) can replace prostate biopsy to guide decisions about whether to remain on AS. We aimed to quantify the performance characteristics of MRI as a potential replacement for biopsy in a large, diverse, national VA cohort. Methods: The study cohort consists of veterans diagnosed with Gleason grade group (GG) 1 or 2 prostate cancer at their diagnostic biopsy undergoing AS. The cohort is further limited to patients that underwent at least one post-diagnosis (confirmatory) biopsy and had at least one MRI with an assigned Prostate Imaging-Reporting and Data System (PI-RADS) score completed within 180 days prior to their confirmatory biopsy (CBx) and/or any subsequent surveillance biopsy (SBx). MRI was evaluated as negative (PI-RADS v2.1 score of 1-2) or positive (PI-RADS score of 3-5) in its ability to predict GG≥2 prostate cancer on post-diagnosis biopsy, vs. either negative or GG1. We focused on the negative predictive value (NPV), given the key clinical question whether MRI can safely replace biopsy, and stratified results by PSAD (< 0.15 ng/mL and >= 0.15 ng/mL) and GG groups (GG1 vs GG2) at diagnosis. Results: We identified 1,662 cases with eligible confirmatory biopsies and 796 cases with eligible surveillance biopsies among 2,188 patients. Biopsies were from patients with a median age of 67 with 80% having GG1 cancer at their diagnostic biopsy and the remaining 20% at GG2. The negative predictive value (NPV) was 74% for all confirmatory biopsies and 75% for subsequent surveillance biopsies. Performance was worse in some contexts: for example, among patients with GG2 at diagnosis, NPV was only 38% at the confirmatory biopsy and 60% at subsequent surveillance biopsies. On the other hand, for those with PSAD less than 0.15 ng/mL, NPV at the surveillance biopsy was 82% (Table). Conclusions: Negative MRI—as defined by PI-RADS 1-2—does not consistently rule out the presence of GG≥2 prostate cancer and therefore cannot safely replace confirmatory biopsy. In some contexts (e.g., subsequent surveillance biopsy for patients with low PSAD) MRI may be an adequate surrogate. Group Type of Biopsy Count NPV PPV Sensitivity Specificity Overall CBx 1,662 0.74 0.53 0.96 0.13 Overall SBx 796 0.75 0.52 0.97 0.10 GG1 CBx 1,317 0.79 0.49 0.96 0.14 GG1 SBx 672 0.77 0.48 0.96 0.10 GG2 CBx 345 0.38 0.69 0.96 0.06 GG2 SBx 124 0.60 0.72 0.98 0.08 Low PSAD CBx 755 0.78 0.60 0.98 0.10 Low PSAD SBx 382 0.60 0.61 0.96 0.08 High PSAD CBx 693 0.75 0.43 0.93 0.15 High PSAD SBx 309 0.82 0.42 0.96 0.12