PSMA PET predicts metastasis-free survival in the setting of salvage radiotherapy after radical prostatectomy

INTRODUCTION: To evaluate the impact of PSMA PET (prostate specific membrane antigen positron emission tomography) findings prior to salvage radiotherapy (SRT) in recurrent prostate cancer (PCa) after radical prostatectomy (RP) on metastasis-free survival (MFS).

PATIENTS AND METHODS: Between 01/2012 and 12/2018, 1,599 patients received SRT for biochemical recurrence after RP at our institution. Five-year MFS of "positive PSMA PET" (n = 49) vs. "negative PSMA PET" (n = 106) vs. "no PSMA PET" (n = 1,599) prior to SRT was determined. For all time to event analyses, uni- and multivariable Cox's proportional hazards models and univariable Kaplan-Meier analyses were applied, with a significance threshold of P < 0.05. Further 4:1 propensity score matching for patient, cancer and treatment characteristics was performed to account for residual differences between groups.

RESULTS: Of PSMA PET patients, 106 patients exhibited "negative PSMA PET" (68.4%) and 49 exhibited "positive PSMA PET" (31.6%). Median PSA at recurrence did not differ between groups (0.2 ng/ml; P= 0.4). After 4:1 propensity score matching, 5-year MFS between "no PSMA PET" and "negative PSMA PET" was 94.4 vs. 93.0%, respectively (P = 0.8). For "no PSMA PET" versus "positive PSMA PET", 5-year MFS was significantly lower in "positive PSMA PET" (92.3 vs. 48.5%, respectively P < 0.0001). Finally, "positive PSMA PET" was independently associated with worse MFS compared to "no PSMA PET" after multivariable adjustment in the overall cohort (HR 13.8, CI 7.5-25.2, P < 0.001).

CONCLUSIONS: Locoregional positive PSMA PET findings in recurrent patients after RP are highly predictive of worse MFS in the setting of SRT.