Diagnostic Performance of 68 Ga-PSMA-11 Positron Emission Tomography/Computed Tomography to Monitor Treatment Response in Patients with Metastatic Prostate Cancer: The Concordance Between Biochemical Response and Prostate-specific Membrane Antigen Results

Treatment response is traditionally monitored using prostate-specific antigen (PSA) and conventional imaging in patients with metastatic prostate cancer (mPCa). To assess the diagnostic performance of prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) when monitoring mPCa patients receiving systemic treatment and also to investigate the concordance between PSMA PET response according to the PSMA PET progression (PPP) criteria and biochemical response. A total of 96 patients with Ga-PSMA-11 PET/CT-detected mPCa at baseline PSMA PET/CT (bPSMA) who underwent at least one follow-up scan after receiving systemic treatment were included in the study. PSA levels at bPSMA and follow-up PSMA PET (fPSMA) scans were recorded. The PPP criteria were used to define PSMA progression. Biochemical progression was defined as ≥25% increase in PSA. PSMA PET and PSA responses were dichotomized into progressive disease (PD) versus non-PD, and the concordance between PSA and PSMA responses was evaluated. The concordance between PSA and PSMA PET responses was presented using frequencies, percentages, and Cohen's kappa test. A total of 345 serial PSMA PET/CT (96 bPSMA and 249 fPSMA) scans were evaluated. The positivity rates of PSMA PET scans for PSA levels of 4 ng/ml were 55.6%, 75.0%, 100%, and 98.8%, respectively. PSA and PSMA responses showed moderate-to-high concordance (Cohen's κ = 0.623, p