[⁶⁸Ga]Ga-PSMA-11 PET Tumor Volume Predicts Overall Survival of Patients with Metastatic Prostate Cancer Undergoing Taxane-Based Chemotherapy

Prostate-specific membrane antigen (PSMA) PET has the potential to monitor the response to taxane-based chemotherapy in patients with prostate cancer and shows promise for predicting outcomes and improving response evaluation. This retrospective study aimed to determine the prognostic value of [68Ga]Ga-PSMA-11 PET (PSMA PET)-derived quantitative tumor burden parameters for overall survival (OS). Methods: Databases from 6 institutions were screened for patients with prostate cancer who underwent PSMA PET and whose serum prostate-specific antigen (PSA) measurements were recorded at baseline and after completing taxane-based chemotherapy. Tumor segmentation was performed using artificial intelligence-based software, and PSMA PET whole-body quantitative parameters were obtained, including PSMA-positive tumor volume (PSMA-VOL), SUVmax, and SUVmean Univariate Cox regression analyses were used to evaluate the association of whole-body quantitative PSMA parameters and PSA levels with OS. The Harrell concordance index (C-index) was used to determine prognostic accuracy. Optimal cutoffs were determined by maximizing the log-rank statistic. Results: In total, 128 patients were included in the study; 62 (48%) had hormone-sensitive prostate cancer, and 66 (52%) had castration-resistant prostate cancer. At baseline, PSMA-VOL had the highest prognostic value for OS compared with serum PSA, SUVmax, and SUVmean (C-index of 0.88, 0.80, 0.69, and 0.29, respectively), whereas the percentage change in PSA levels had the highest prognostic value during treatment compared with percentage change in PSMA-VOL, SUVmax, and SUVmean (C-index of 0.94, 0.85, 0.90, and 0.85, respectively). Conclusion: Baseline and posttherapeutic PSMA PET quantitative parameters are prognostic for OS after taxane-based chemotherapy in patients with metastatic prostate cancer. Baseline PSMA-VOL had the highest prognostic value for OS, whereas changes in PSA levels outperformed changes in quantitative PSMA PET parameters during treatment.