ASCO 2023: PSMA PET Guided Salvage Radiotherapy Among Patients with Prostate Cancer in the Post-Prostatectomy Setting: A Single Center Post-Hoc Analysis

( The 2023 American Society of Clinical Oncology (ASCO) annual meeting held in Chicago, IL between June 2nd and June 6th was host to a prostate, testicular, and penile cancers poster discussion session. Dr. Jeremie Calais presented the results of a single center post-hoc analysis evaluating PSMA-PET/CT-guided salvage radiotherapy among patients with prostate cancer in the post-prostatectomy setting.

PSMA-PET/CT has demonstrated improved sensitivity and specificity, compared to conventional imaging, for the detection of locoregional and distant disease in the biochemical recurrence setting. The proPSMA trial demonstrated that 68Ga-PSMA-11 PET/CT was superior to conventional imaging for the detection of pelvic nodal (AUC: 91% versus 59%) and distant metastases (AUC: 95% versus 74%).1 Use of PSMA-PET/CT in the biochemical recurrence setting has been shown to change planned management for these patients; however, whether PSMA-PET/CT-guided management decisions improve oncologic outcomes remains to be determined. As such, Dr. Calais and colleagues aimed to evaluate the outcomes of patients with biochemical recurrence post-radical prostatectomy who received PSMA-PET/CT-guided salvage radiotherapy.

This was a post-hoc analysis of five prospective studies of PSMA-PET/CT conducted at UCLA between 2016 and 2021. Patients were inclusion eligible if they:

  • Had biochemical recurrence post-radical prostatectomy
  • Initiated salvage radiotherapy within 3 months of PSMA-PET/CT
  • Did not receive salvage radiotherapy with palliative intent
  • Had at least 12 months of follow-up following completion of salvage radiotherapy
  • Had treatment details available
  • Did not have distant metastases by conventional imaging on upfront staging

Metastasis-directed therapy was defined as salvage radiotherapy to all PSMA+ N1 and M1 lesions. Biochemical relapse following salvage radiotherapy was defined as a PSA increase of ≥0.2 ng/ml above post-salvage radiotherapy nadir. Biochemical relapse rates post-salvage radiotherapy were estimated using Kaplan Meier curves.

This study included 175 patients. The median time between radical prostatectomy and PSMA-PET/CT was 38 months (range: 1 – 329 months). The median PSA at time of imaging was 0.63 ng/ml (range: 0.063 – 35).

patient population

PSMA PET was positive in 128/175 patients (73%), with a median of 1 lesion per positive scan:

  • miT+N0M0: 12%
  • miTxN1M0: 31%
  • miTxNxM1: 30%
    • M1a: 11%
    • M1b: 18%
    • M1c: 1%

PSMA-PET/CT-guided salvage radiotherapy treatments were as follows:

  • Prostate bed only: 22%
  • Prostate bed + pelvic nodes: 34%
  • Pelvic nodes only: 19%
  • Prostate bed + pelvic nodes + distant metastases: 4%
  • Pelvic nodes + distant metastases: 4%
  • Distant metastases only: 18%

treatment details

Concurrent ADT was administered to 59/175 (34%) patients with a median treatment duration of 6 months. At a median follow-up of 32 months (range 12-70) after salvage radiotherapy, outcomes were as follows:

  • No evidence of biochemical or imaging relapse: 45%
  • Biochemical, but no imaging relapse: 14%
  • Both biochemical and imaging relapse: 40%
  • Imaging relapse only: <1%

recurrence details

The median time to biochemical and imaging relapses post-salvage radiotherapy were 15 and 19 months, respectively. 23% of patients had biochemical recurrence one-year post-salvage radiotherapy.

PFS stage graphs

Of the 83 patients treated with MDT, 32 (39%) did not develop subsequent disease relapse.

recurrence rate flow

Dr. Calais concluded that this post-hoc analysis demonstrates that PSMA-PET/CT-guided salvage radiotherapy is an effective method for treating both locoregional and distant recurrences. Further investigation is needed to assess the full extent of patient outcomes in this population.

Presented by: Jeremie Calais, MD, MSc, Associate Professor of Nuclear Medicine and Theranostics, Department of Molecular and Medical Pharmacology, University of California, Los Angeles, CA

Written by: Rashid Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2023 American Society of Clinical Oncology (ASCO) Annual Meeting, Chicago, IL, Fri, June 2 – Tues, June 6, 2023.

  1. Hofman MS, Lawrentschuk N, Francis, RJ, et al. Prostate-specific membrane antigen PET-CT in patients with high-risk prostate cancer before curative-intent surgery or radiotherapy (proPSMA): A prospective, randomized, multicentre study. Lancet 2020 Apr 11;395(10231):1208-1216.