⁶⁸Ga-PSMA-11 PET/CT in recurrent prostate cancer: efficacy in different clinical stages of PSA failure after radical therapy

Objectives: The primary objective was the evaluation of Gallium 68 (⁶⁸Ga)-prostate-specific membrane antigen (PSMA)-11 positron emission tomography/computed tomography (PET/CT) detection rate, for identifying the site of prostate cancer (PCa) relapse (local vs systemic), stratifying the population according to different clinical stages of biochemical recurrence (BCR). Secondary aims were: 1) to evaluate the association of clinical/pathologic features and ⁶⁸Ga-PSMA-11 PET/CT detection rate, 2) to compare ⁶⁸Ga-PSMA-11 PET/CT with other imaging procedures, and 3) to evaluate the positive predictive value (PPV) in a per-patient analysis.

Material and methods: This population was enrolled through a prospective, open label, single-center trial performed at the Nuclear Medicine of the University Hospital of Bologna (Eudract: 2015-004589-27 OsSC). The inclusion criteria were: (1) proven PCa, (2) surgery or radiotherapy as definitive therapy, (3) proven BCR, (4) prostate-specific antigen (PSA) 0.2-2 ng/ml, (5) age ≥ 35 years, and 6() willing to sign an informed consent. Three-hundred and thirty-two (332) patients were enrolled between March 2016 and June 2017; mean/median PSA was 0.84/0.61 ng/ml, 97.9% (325/332) of patients received radical prostatectomy and 2.1% (7/332) radiotherapy. Different patterns of BCR were identified by referent physicians as follows: (a) persisting detectable PSA after radical prostatectomy in 13.5% (45/332) of patients (subgroup 1), (b) first-time PSA failure after radical therapy in 44.9% (149/332) (subgroup 2), and (c) PSA increase after salvage or hormonal therapy in 41.6% (138/332) (subgroup 3).

Results: Primary objective: ⁶⁸Ga-PSMA-11 PET/CT detection rate was 53.6% (CI 95% 48.1%-59.1%). In a patient-based analysis, disease confined to pelvis (prostate bed and/or lymph-nodes) was detected in 24.7% of cases (82/332). The presence of at least one distant lesion was observed in 28.9% of cases (96/332). The detection rate in different subgroups was: subgroup 1 = 64.5%, subgroup 2 = 45.6%, and subgroup-3 = 58.7%. Secondary objectives: 1) PSA (p = 0.041) and PSAdt (p = 0.001) showed association with ⁶⁸Ga-PSMA-11 PET/CT detection rate, and 2) correlative imaging was available in 73.2% of patients (243/332). When ⁶⁸Ga-PSMA-11 PET/CT was positive, correlative imaging resulted negative in 83% of cases (108/130). 3) The calculated PPV was 96.2%.

Conclusion: Our data confirmed the efficacy of ⁶⁸Ga-PSMA-11 PET/CT for detecting local vs systemic disease in PCa patients presenting PSA failure after radical therapy. Furthermore, ⁶⁸Ga-PSMA-11 PET/CT detection rate is different depending on the clinical stage of BCR, and this information should be taken into consideration by referring physicians.