Impact of 68Ga-PSMA-11 PET/CT on Initial Staging of High-Risk Prostate Cancer Patients: Post-Hoc Analysis of a Prospective Single Center Experience

Abstract

Conventional imaging for initial staging of prostate cancer (PCa) lacks sensitivity and underestimates disease burden. Prostate-specific membrane antigen PET/CT (PSMA PET) is an emerging imaging modality shown to have improved sensitivity over conventional imaging in the setting of biochemical recurrence. We sought to evaluate the impact of 68Ga-PSMA PET on initial staging of patients with high risk PCa, as well as clinicopathologic features that might predict for upstaging, by analyzing patients who prospectively underwent PSMA PET on a clinical trial. This was a post hoc analysis of 249 eligible patients with NCCN high/very high risk PCa who underwent a staging PSMA PET (12/2016 to 1/2020) on a prospective trial. Patients with known non-regional lymph node or distant metastasis on prior imaging, or initiation of androgen deprivation therapy more than 3 months before PSMA PET were excluded. Chi square analysis was used to evaluate the association of clinicopathologic features (Gleason grade group [GG], initial PSA [iPSA], T stage, percent positive cores [PPC]≥50%) with upstaging. Overall, 22.9% patients were upstaged by PSMA PET; 18.9% of patients with iN0 disease by CT or MRI were found to have N1 disease by PSMA PET, and 10.6% of patients who had M0 disease by CT or bone scan had M1 disease by PSMA PET. New M1a disease was found in 7.4% and M1b/M1c disease was found in 5.3% of patients. PSMA PET detected ECE, SVI or invasion of surrounding structures in 8.1% patients deemed T2 on prior MRI imaging. PPC≥50% was significantly associated with regional and any nodal upstage (23.9% vs. 12.1%, p = 0.0227 and 22.6% vs. 3.7%, p = 0.0261, respectively), and any upstage in general (29.3% vs. 14.6%, p = 0.0102). Patients with GG 5 or ≥50% PPC were more likely to have regional nodal upstage (23.4% vs. 6.3%, p = 0.0031) and any upstage in general (28.2% vs. 9.4%, p = 0.0024), while GG 5 together with ≥50% PPC was predictive of M stage upstage (23.3% vs. 4.7%, p = 0.0063). cT and iPSA were not associated with upstaging. PSMA PET/CT has a significant impact on initial staging of high risk PCa patients. This impact appears to be most marked in patients with GG 5 or PPC≥50%.