PSMA PET versus conventional imaging in metastatic prostate cancer: Evaluation of disease volume classification in a veteran cohort.

21 Background: Conventional imaging (CI), including CT and bone scans, has traditionally guided treatment decisions for patients with metastatic prostate cancer (mPCa). In the CHAARTED trial, a binary low/high-volume disease classification system was established using CI. However, the emergence of PSMA PET imaging, which can detect lesions previously unseen on CI, has complicated the use of disease volume classification to guide therapy. This study assessed the impact of PSMA PET on disease volume classification and treatment selection in mPCa patients at a single VA medical center. Methods: This retrospective study included veterans with mPCa who underwent PSMA PET imaging at the James J. Peters VA Medical Center. Metastatic disease was defined as ≥1 extra-pelvic PSMA-avid lesion. CHAARTED volume status was retrospectively assigned using both PSMA and CI data. Descriptive statistics and paired comparisons were conducted in R, and p<0.05 was considered significant. Results: A total of 75 patients were included (median age 77, IQR 15.5; 71% Black). Forty-two had CI within 3 months of PSMA PET, and 90% (38/42) had more lesions detected on PSMA. By CHAARTED criteria, 29% (12/42) were high-volume by CI, compared to 62% (26/42) by PSMA. Among CI low-volume patients, 50% (15/30) were upstaged by PSMA. Concordant high-volume patients demonstrated more advanced disease, with higher PSA (p=0.017) and lower 1-year survival (p=0.028) compared to concordant low-volume patients, while discordant cases (PSMA-high/CI-low) were intermediate. Chemotherapy use post-PSMA was low (8%), with androgen deprivation therapy (ADT) plus novel hormonal therapy (NHT) the most common treatment combination (31%). Conclusions: PSMA PET identified more metastatic lesions and more frequently classified disease as high-volume compared to CI. Concordant high-volume patients had the poorest outcomes, concordant low-volume the most favorable, and discordant patients were intermediate, suggesting that PSMA-informed classification may have improved prognostic value compared to CI. Despite more frequent upstaging, chemotherapy use remained uncommon, likely reflecting comorbidity burden and clinical preference for NHT. These findings, from a predominantly Black veteran cohort underrepresented in prostate cancer research, highlight the need for larger multi-institutional studies to validate the prognostic value of PSMA-guided disease stratification and ensure its generalizability across diverse populations. Clinical characteristics by CI–PSMA concordance. Variable Concordant High Discordant High (PSMA-high/CI-low) Concordant Low p-value N 11 15 15 - PSA, median (IQR) 246 (123–501) 86 (19.5–190) 28 (11.8–69.4) 0.017* Gleason, median (IQR) 9 (7.5–9) 8 (7–8.5) 7 (6.5–9) 0.926 1-year overall survival — % (95% CI) 45 (24–87) 53 (33–86) 87 (71–100) 0.028* *Indicates p < 0.05.