68Ga-PSMA-11 PET/CT Versus Conventional Imaging for Response Evaluation in Metastatic Castration-resistant Prostate Cancer: A Single-center Prospective Study.

[PURPOSE] Patients with metastatic castration-resistant prostate cancer (mCRPC) often undergo multiple treatments, making accurate response assessment vital. The conventional imaging-based PCWG3 criteria, incorporating the RECIST-1.1, have been the gold standard so far. Although 68Ga-PSMA-11-PET/CT has shown an incremental role in staging of prostate cancer, its utility in response evaluation lacks prospective validation. Here, we prospectively evaluate different 68Ga-PSMA-11-PET/CT-based response evaluation criteria, including RECIP-1.0, PPP, and aPERCIST, and compare these with the PCWG3 criteria.

[METHODS] mCRPC patients, initiating treatment with taxanes, androgen-receptor pathway inhibitors (ARPIs), or 177Lu-PSMA-617, underwent 68Ga-PSMA-11-PET/CT and conventional imaging (CECT and bone scintigraphy) at baseline, and every 12 weeks after treatment.

[RESULTS] Thirty-four mCRPC patients were included (median age: 68.5 y, median PSA: 61.9 ng/mL). Nonprogression rates at 12 weeks according to PCWG3, aPERCIST, PPP, and RECIP-1.0 were 23.5%, 8.8%, 17.6%, and 23.5%, respectively. The highest inter-reader agreement was observed with RECIP-1.0 (κ=0.84). The median OS was 16.5 months with nonprogression according to PCWG3 being associated with significantly better OS (P=0.02), and no significant associations were observed with the rest of the criteria. In surrogacy analysis of rPFS for OS in the overall cohort, the highest C-index was observed for PCWG3-rPFS (C=0.72), followed by RECIP-rPFS (C=0.71). In subgroup analyses, RECIP-rPFS had the highest C-index for non-ARPI patients (C=0.76), and PCWG3-rPFS for the ARPI patients (C=0.75).

[CONCLUSIONS] PCWG3 remains the most effective response criterion overall and for ARPI-treated patients, while RECIP-1.0 showed better prognostic value for non-ARPI patients. Larger studies are needed to validate these findings.