PSMA PET “highly predictive” of MFS after salvage RT for biochemical recurrence

PSMA-PET imaging results are “highly predictive” of metastasis-free survival (MFS) outcomes in patients who received radical prostatectomy (RP) for localized prostate cancer followed by salvage radiotherapy (SRT) for biochemical recurrence, according to a retrospective analysis shared during the 36th Annual European Association of Urology Congress.¹ 

“Previous studies on PSMA PET prior to SRT after RP provide short-term biochemical response rates. Biochemical recurrence usually precedes development of metastasis by several years,” explained study investigator Christoph Würnschimmel, MD, Martini-Klinik Prostate Cancer Center, University Hospital Hamburg-Eppendorf, Hamburg, Germany. “Our study provides a large and contemporary report that provides 5-year MFS rates after SRT, stratified by PSMA PET results.”

Between 2012 and 2018, 1752 patients received SRT for biochemical recurrence (>.2 ng/mL) or PSA persistence after RP. All RPs were performed at the Martini-Klinik center. All patients were treated with SRT to the prostatic fossa and/or locoregional pelvic lymph nodes. No patients had metastatic disease.

Patient were stratified by “no PSMA PET,” “PSMA positive,” and “PSMA negative.” Univariable Kaplan-Meier analyses displayed 5-year MFS. Cox proportional hazards models calculated the independent association of PSMA findings on MFS.

Of the 1752 patients, 1571 patients received no PSMA PET and 94.3% of these patients received SRT of prostatic fossa only. There were 123 patients who had negative PSMA PET, and 82.1% of these patients had SRT of prostatic fossa only. And 58 patients had positive PSMA PET, 96.6% of whom received SRT of prostatic fossa only.

Würnschimmel noted that the median PSA at recurrence did not vary between the groups (0.2 ng/mL; P = .4).

In general, patients with positive PSMA PET had the worst tumor characteristics, including the highest rates of stage ≥pT3 disease (65.5%) and Gleason grade group 5 (17.2%). The median PSA at RP in this group was highest at 9.7 ng/mL, as was the median tumor volume (7.3 mL). Additionally, these patients had the highest rates of neoadjuvant androgen-deprivation therapy (ADT) during RP (10.3%), PSA persistence after RP (15.5%), and concomitant ADT during SRT (55.2%). They also had the shortest time to SRT at 16.9 months.

Patients with negative PSMA PET had the most favorable tumor characteristics. Overall, 54.5% of patients in this subgroup had ≥pT3 disease and 8.1% were Gleason grade group 5. The median PSA at RP was 8.0 ng/mL and the median tumor volume was 5.2 mL. The rates of neoadjuvant ADT, PSA persistence, and concomitant ADT during SRT were 9.8%, 13.8%, and 47.2%, respectively. The median time to SRT was 29.4 months.

The no PSMA PET patients demonstrated tumor characteristics that were “intermediate between the negative and positive PSMA PET groups,” said Würnschimmel. The rates of neoadjuvant ADT, PSA persistence, and concomitant ADT during SRT in this group were 8.0%, 8.1%, and 25.1%, respectively. These patients had the second longest median time to SRT at 21.7 months.

The key study findings showed that the 5-year MFS rates for no PSMA PET versus negative PSMA PET were 94.5% versus 90.6%, respectively, and did not differ in multivariable analysis (P = .2). In contrast, the 5-year MFS for no PSMA PET versus positive PSMA PET significantly differed at 92.7% versus 38.2%, respectively (P <.001).

“This confirms the potential of PSMA PET to distinguish between risk groups for MFS,” said Würnschimmel.

Würnschimmel did note some limitations of the study, including the small size of the positive PSMA subgroup, the lack of standard imaging routines during follow-up, and the lack of available explicit radiologic information on disease burden.

Reference

1. Wenzel M, Hussein R, Graefen M, Tilki D, Tobias T, Würnschimmel C. Long-term validation on the impact of PSMA-PET on metastasis-free survival in a large salvage radiotherapy cohort. Presented at 36th Annual EAU Congress (virtual). July 8-12, 2021. P1175.