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

Introduction: This study aimed to assess the detection rate of prostate cancer recurrence by prostate-specific member antigen positron emission tomography/computed tomography (PSMA PET/CT) with ¹⁸F-DCFPyL in patients with residual disease or biochemical recurrence (BCR), and its association with surgical pathology and prostate-specific antigen (PSA) kinetics.

Methods: Men from South Central Ontario enrolled in the PSMA Registry for Recurrent Prostate cancer (PREP) between April 2019 and December 2021 after radical prostatectomy (RP) and who had 1) pathologic stage N1 or persistent elevated PSA; or 2) BCR (PSA >0.10 ng/mL) where initial postoperative PSA was undetectable were included.

Results: A total of 169 men (median age 68 years; interquartile range [IQR] 62-71) with complete data met the above criteria. The median PSA was 0.27 ng/mL (IQR 0.16-0.85) prior to PSMA-PET. Overall positivity rate 59%; when PSA was <0.40 ng/mL, overall positivity rate 42% vs. 85% with PSA ≥0.40 ng/mL (p<0.001). Higher pathologic tumor stage increased detection of regional lymph nodes (LN) (pT2-3a: 32% vs. pT3b: 69%, p<0.001) but not distant metastases (pT2-3a: 12% vs. pT3b: 24%, p=0.15). PSMA-PET detected 18% with prostate bed, 42% with regional LN disease, and 44% with pelvic-only disease. The three most involved LN chains were the internal (21%) and external (20%) iliac, and obturator chains (16%).

Conclusions: This prospective study of patients with residual disease or BCR after RP illustrates patterns of failure that could impact diagnosis and postoperative management. Such patients have significant risk of regional LN positivity on PSMA-PET highlighting a need to include pelvic LN within salvage radiotherapy volumes.