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

Abstract

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