Comparative assessment of METastasis Reporting and Data System for Prostate Cancer versus Prostate Cancer Clinical Trials Working Group 3 Criteria in assessing treatment response in patients with metastatic castration-resistant prostate cancer

Background Unequivocal clinical progression without radiological progression according to Prostate Cancer Clinical Trials Working Group 3 (PCWG3) criteria is recognised in metastatic castration-resistant prostate cancer (mCRPC), reflecting limitations of bone scintigraphy in distinguishing an osteoblastic progression from an osteoblastic flare. Objective To compare the METastasis Reporting and Data System for Prostate Cancer (MET-RADS-P) on whole-body magnetic resonance imaging (WBMRI) with PCWG3 imaging criteria, the current gold standard. Design, setting, and participants A retrospective cohort of 184 patients with mCRPC who underwent paired WBMRI and conventional imaging during therapy. Outcome measurements and statistical analysis The primary endpoint was concordance (percentage agreement [%A]) between MET-RADS-P and PCWG3 for overall, bone-only, and soft-tissue-only responses. Secondary endpoints were radiologic progression-free survival (rPFS) by each system and overall survival (OS) according to early (≤12 wk) MET-RADS-P response. Results and limitations We evaluated 467 paired assessments in 184 patients. Overall concordance between PCWG3 and MET-RADS-P was moderate (%A = 64.5%; 95% confidence interval [CI] = 59.8–68.7), and it was high in soft tissue (%A = 88.8%; 95% CI = 85.7–91.6) and limited in bone (%A = 44.4%; 95% CI = 39.8–48.9). MET-RADS-P labelled progression more often than PCWG3 overall (66.6% vs 39.7%) and in bone (61.2% vs 20.3%). Median rPFS was shorter by MET-RADS-P than by PCWG3 (2.7 vs 4.2 mo; p < 0.001). Early MET-RADS-P progression was significantly associated with worse OS (adjusted hazard ratio [HR] = 4.75; 95% CI = 2.1–10.7; p < 0.001). Limitations include retrospective single-centre design, trial-based expert-centre cohort, and limited follow-up. Conclusions Concordance between PCWG3 and MET-RADS-P was moderate overall and limited in bone. Earlier MET-RADS-P–defined progression may identify aggressive disease and allow a prompt change in therapy before clinical deterioration limits subsequent treatment options. Prospective validation is warranted.