Background
Prostate Specific Membrane Antigen (PSMA) PET/CT imaging is increasingly used to stage metastatic prostate cancer (mPC). Increased PSMA avidity is correlated with higher-grade disease and poorer prognosis. The role of PSMA avid tumour burden in predicting survival outcomes remains unclear to date. We aimed to investigate PSMA avid tumour burden as a potential prognostic biomarker in mPC.
Methods
Following HREC approval, mPC patients receiving androgen deprivation therapy (ADT) who underwent [68Ga]Ga-PSMA-11 PET/CT within 3 months of treatment initiation were identified at Royal North Shore Hospital, Australia (2014-2019). Patients were collected as two cohorts; Cohort 1 received ADT + further systemic therapy (docetaxel, enzalutamide or abiraterone); Cohort 2 received ADT alone.
Images were analysed using MIM software (version 6.8.3) and lesions above a flat SUV threshold of 4 were validated by nuclear medicine physician review and were included for analysis. Relevant clinicopathologic variables, clinical outcomes (progression-free and overall survival), and PSMA avid tumour burden (total, primary, metastatic) were collected. Each cohort was dichotomized by the median tumour burden, with groups compared using the log-rank test.
Results
Ninety-eight patients were identified (cohort 1: 15, cohort 2: 83). For cohort 1, median age at diagnosis was 71 years, and the median Gleason Score was 7. Ten (67%) were treated with ADT and docetaxel with the others treated with ADT and novel anti-androgenics. The median total PSMA-avid tumour burden was 119.2mL (IQR 12.3-252.2). Appreciating the small number of patients in cohort 1, there was no significant difference in PFS between those above and below the median total PSMA avid tumour burden (P= 0.3).
Conclusion
Here we describe the relationship between clinical outcomes and PSMA PET scan findings in patients with newly diagnosed mPC. Further data concerning overall survival analysis and cohort 2 will be presented at the meeting.