MRI Can Replace Early Protocol Biopsy in Patients Undergoing Focal Cryoablation for Prostate Cancer

Introduction and Objectives: Assessing oncological success following focal ablation for prostate cancer (PCa) includes prostate-specific antigen (PSA) response and imaging. However, the value of protocol biopsy remains uncertain. Consensus recommendations include follow-up multiparametric MRI (mpMRI) and biopsy despite variable imaging quality, interpretation, and biopsy performance. We aim to determine mpMRI performance characteristics postablation for early in-field (within the ablation zone) failure following focal cryoablation (FC). Methods: Patients receiving FC from January 1, 2017, to April 21, 2023, at Michigan Medicine were enrolled in a multi-institutional, institutional review board-approved prospective registry. Per protocol, PSA, mpMRI, and ultrasound-MR fusion biopsy of the ablation bed were obtained at 6 to 12 months postablation. Residual PCa was suspected on mpMRI if there was persistent enhancement and impeded diffusion near the ablation zone colocalizing to the intended ablation target. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of postablation mpMRI for Gleason Grade Group (GG) ≥2 PCa were calculated. Chi-squared test was used to perform bivariate analysis. Results: A total of 76 patients underwent primary ablation, postablation mpMRI, and protocol biopsy. Eight patients underwent repeat cryoablation with postsalvage cryoablation mpMRI and biopsy (N = 84 postablation events). Postablation mpMRI showed persistent PCa in 13.4% (11/84). Postablation biopsy showed GG ≥2 PCa in 7.1% (6/84) of target lesions. MpMRI sensitivity, specificity, PPV, and NPV for detecting untreated GG ≥2 PCa postablation were 83.3%, 92.3%, 45.5%, and 98.6%, respectively, with significant association between positive MRI and biopsy detection of GG ≥2 PCa (p < 0.0001). The positive and negative likelihood ratios for residual disease detection were 10.8 and 0.18. Conclusion: Postablation mpMRI has a high sensitivity, NPV, and specificity for detecting untreated GG ≥2 PCa. If negative, near-term "protocol" biopsy may be safely avoided. Investigation into causes of false positive and negative postablation mpMRI will help identify those who warrant per-protocol biopsy.