Impact of PSMA PET staging on prognosis for radiologically node-positive prostate cancer

Abstract

Purpose: Node-positive prostate cancer is considered Stage IV disease in the current AJCC staging system. These patients may therefore be treated nihilistically and denied potentially curative treatment. Prostate-specific membrane antigen positron emission tomography (PSMA PET) is now accepted as a more sensitive staging modality which can detect nodal disease that would not have been identified using conventional imaging. To date, no studies have been performed to confirm whether PSMA PET staging confers a better prognosis for node-positive prostate cancer compared to patients with node-positive disease identified on conventional imaging.

Methods and Materials: Since 2015, PSMA PET scanning has been used for staging men with prostate cancer at the Northern Sydney and Central Coast Cancer Centres. All patients with node-positive prostate cancer and disease confined to the pelvis based on conventional or PSMA PET imaging, who were treated definitively with combination androgen deprivation therapy and dose-escalated radiation treatment to the prostate and pelvic lymph nodes since 2007 were included. Kaplan-Meier and Cox regression analysis was used to compare cumulative incidence of biochemical failure (BF) between patients who were staged with PSMA PET versus conventional imaging.

Results: Seventy-six men with pelvic nodal metastases were identified. Fifty-one was staged with PSMA PET while 25 were staged using only conventional imaging. Median follow-up was 4.5 years. Cumulative incidence of BF at 4 years was 29% with PSMA PET-staged patients vs 58% with conventionally staged patients (Hazard Ratio 2.7, 95%CI 1.35, 5.43, P=0.005). Incidence of BF at 4 years in Gleason Score 7 patients were 17% at 4 years vs 42% for Gleason score 8-10 patients. On multivariate analysis, PSMA PET staging was found to be associated with lower rates of BF (HR=6.91, 95%CI 1.4, 34.2, P=0.006).

Conclusion: Men with PSMA PET-staged node-positive prostate cancer have significantly better biochemical control compared to node-positive disease identified on conventional staging. The subset of patients with Gleason score 7 node-positive disease identified on PSMA-PET had low rates of biochemical failure. Curative intent treatment with combined modality therapy should be offered to node-positive patients.