Patterns of failure with 18F-DCFPyL PSMA PET/CT in the post-prostatectomy setting: A regional cohort analysis.

309 Background: The participants are patients enrolled in the PSMA-PET Registry for Recurrent Prostate Cancer (PREP) who were referred for [18F]-DCFPyL PET/CT at our institution in Hamilton, Canada. The Registry is the only funded access to PSMA PET/CT for patients in Ontario. Methods: Our analysis includes all men who had a PSMA PET/CT on the Registry between April 2019 and December 2021 and are either node positive, or persistently detectable PSA after initial radical prostatectomy (RP), or biochemical failure after initial RP. Results: In total 177 men were enrolled on the Registry who met the above criteria. 170 men had complete pathological information available and were included. The pre-PSMA PET/CT median PSA was 0.27 ng/mL. Overall, the probability of a positive PSMA PET/CT result was 59.4%, and the incidence increased with increasing PSA. Lymph node (LN) and distant metastases (DM) were detected more frequently in patients with Grade groups 3-5 and higher pathologic tumor (pT) and nodal (pN1) disease. Across all 170 patients the most common site for LN recurrence was in the internal iliac chain (15.9%), followed by the external iliac (14.7%), obturator (11.8%), common iliac (10.0%), pre-sacral (8.8%), para-aortic (7.7%), and peri-rectal (5.9%) chains. The PSMA PET/CT recurrence rate, PSA, and pathological tumor stage is reported, with the location of the recurrence indicated. Conclusions: Our prospective study elucidates patterns of failure for prostate cancer patients with biochemical recurrence after RP and could impact management at diagnosis and after RP. There is a significant risk of pelvic LN positivity on PSMA PET/CT, which emphasizes the importance of including pelvic LNs within salvage radiation volumes. [Table: see text]