Abstract
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Introduction: Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) is becoming standard of care for men with biochemical recurrence (BCR) of prostate cancer. The implications of a negative PSMA PET/CT scan in this population remain unclear. This study aims to assess the outcome of patients with BCR post radical prostatectomy (RP) who have negative [18F]DCFPyL PET/CT scan at relapse.
Methods: This post-hoc subgroup analysis is based on a prospective clinical trial. One hundred and one BCR patients (median age, 75 years) with BCR after RP, who tested negative on [18F]DCFPyL PET/CT and subsequently underwent salvage radiotherapy (sRT) or were followed without active treatment, were included. Clinical progression-free survival (CPFS) after negative PSMA PET/CT was determined based on follow-up imaging selected as per clinical practice. Uni- and multivariate Cox regression analyses were performed to examine the association of patients' characteristics, tumor-specific variables, and treatment with clinical progression at the last follow-up. Freedom from progression (FFP) at 1-, 2-, and 3-year were reported.
Results: The median PSA level at PET/CT was 0.56 ng/mL (range, 0.4-11.25). Sixty five (64.4%) patients were followed without receiving further treatment, and 36 (35.6%) received sRT (17.8% to the prostate bed only and 17.8% to the prostate bed and pelvic lymph nodes). Seventeen of the sRT patients (17 of 36, 47.2%) received concomitant androgen deprivation therapy (ADT). Subsequent clinical progression was detected in 21 patients (20.8%), with 52.4% in the pelvic lymph nodes, 52.4% in the prostatic fossa, 19.0% in distant lymph nodes, 14.3% in lungs, and 9.5% in bones. The median CPFS was 36.0 months (range, 7.5-71 months) in the entire cohort, with an FFP of 95.0% at 12 months, 86.8% at 24 months, and 76.0% at 36 months. Multivariate Cox regression analysis revealed that an initial International Society of Urological Pathology (ISUP) grade 5 was significantly associated with clinical progression at the last follow-up (hazard ratio, 5.13, P value, 0.04). Furthermore, the receipt of sRT correlated significantly with lower clinical progression at the last follow-up (hazard ratio, 0.20, P value, 0.03), whereas other clinical and tumor-specific parameters did not. Following surveillance-only and sRT, 29.2% (19 of 65) and 5.6% (2 of 36) of patients, respectively, showed clinical progression. In the sRT group, no significant difference was observed in CPFS between patients who underwent sRT to the prostatic fossa versus those who received sRT to the prostatic fossa and pelvic lymph nodes.
Conclusions: This study suggests that salvage radiotherapy is highly effective to decrease or delay clinical progression in patients with biochemical recurrence following radical prostatectomy who have negative PSMA PET/CT scan results. The analysis also underscores the prognostic significance of the initial ISUP grade, with ISUP grade 5 being associated with worse outcomes.
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