Ga-prostate-specific membrane antigen positron emission tomography/computed tomography for patients with favorable intermediate-risk prostate cancer.

Introduction: Current guidelines do not support the use of pretreatment imaging in patients with favorable intermediate-risk prostate cancer. Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) is more accurate than conventional imaging for preoperative staging. We aimed to evaluate whether pretreatment Ga-PSMA PET/CT is beneficial for identifying pathological lymph node involvement (LNI) and adverse pathology among patients with favorable intermediate-risk prostate cancer.

Methods: We reviewed 88 patients with favorable intermediate-risk prostate cancer who underwent Ga-PSMA PET/CT prior to radical prostatectomy and lymph node dissection from 2016-2020. The primary endpoint was the presence of pathological LNI. Association between pretreatment characteristics and outcomes were evaluated.

Results: Preoperative Ga-PSMA PET/CT showed suspicious uptake in lymph nodes in 4/88 patients (5%), hence, 20 patients would need to be scanned to identify a patient with a positive lymph node on imaging. Two patients had pathological LNI, only one of whom showed Ga-PSMA PET/CT uptake prior to surgery. The sensitivity, specificity, positive predictive value, and negative predictive values of Ga-PSMA PET/CT for identifying LNI were 50%, 97%, 25%, and 99%, respectively. After surgery, four patients had evidence of prostate-specific antigen (PSA) persistence. The rate of PSA persistence was higher among patients with LNI on preoperative Ga-PSMA PET/CT (2/4, 50% vs. 2/84, 2%, p=0.009).

Conclusions: Preoperative imaging of favorable intermediate-risk prostate cancer patients using Ga-PSMA PET/CT showed a low yield for identifying patients at higher risk. Consistent with current guidelines, our findings do not support the routine use of PET/CT in this group of patients. Future prospective studies are needed to validate our findings.