(UroToday.com) The 2025 American Society of Clinical Oncology (ASCO) Genitourinary (GU) Annual Symposium held in San Francisco, CA was host to the prostate cancer poster session. Dr. Andrei Gafita presented a study evaluating clinical protocols to monitor the efficacy of [177Lu]Lu-PSMA radiopharmaceutical therapy in metastatic castration-resistant prostate cancer (mCRPC).
The purpose of this study was to assess the prognostic value of post-therapy SPECT/CT and PET/CT by visual Response Evaluation Criteria in PSMA-imaging (RECIP) 1.0 during [177Lu]Lu-PSMA radioligand therapy for mCRPC and to develop an evidence-based clinical protocol to monitor LuPSMA efficacy.
This was a retrospective analysis of mCRPC patients who received at ≥2 cycles of [177Lu]Lu-PSMA-617 or [177Lu]Lu-PSMA-I&T between April 2019 and November 2023. The study investigators interpreted both baseline and interim LuPSMA-SPECT/CT and PSMA-PET/CT results after two cycles of therapy using RECIP 1.0. Changes in PSA levels at 12 weeks were categorized using the Prostate Cancer Working Group 3 (PCWG3) criteria and combined with the RECIP 1.0 reads to determine progression, using a composite classification method incorporating both PSA and RECIP 1.0 results.
The primary study objective was to evaluate the prognostic value of post-therapeutic SPECT by RECIP 1.0 for overall survival. The clinical protocol was developed based on the prognostic accuracy (C-index) of SPECT versus PET and SPECT + PSA versus PET + PSA.
The study design was as follows:
The study flow chart is illustrated below:
Overall, this study included 105 eligible mCRPC patients. Patients with evidence of progressive disease on SPECT had worse overall survival outcomes compared to those RECIP 1.0 stable disease (HR: 2.5, 95% CI: 1.2–5.3, p=0.015) or a partial response (HR: 6.5, 95% CI: 2.7–15.7, p<0.001).
Of the 105 patients, 73 (70%) underwent both a SPECT and PET/CT following 2 cycles of therapy. Tumor progression by SPECT alone, PET alone, SPECT + PSA, and PET + PSA was as follows:
- SPECT alone: 10%
- PET alone: 41%
- SPECT + PSA: 30%
- PET + PSA: 41%
The C-index for SPECT alone was inferior compared to PET alone (concordance: 0.54 versus 0.66; p<0.001), while that for SPECT+PSA did not differ significantly from that for PET+PSA (0.62 versus 0.66; p=0.07).
Dr. Gafita concluded as follows:
- Post-therapeutic SPECT/CT, assessed using RECIP 1.0 and performed after 2 cycles of [177Lu]Lu-PSMA, is prognostic for overall survival and can be used to evaluate for treatment response
- PSMA-PET/CT identified a significantly higher number of patients with progressive disease, compared to LuPSMA-SPECT/CT
- A composite classification system of SPECT/CT + PSA achieved a similar prognostic accuracy, compared to interim PSMA-PET/CT+ PSA for response evaluation during [177Lu]Lu-PSMA treatment
Presented by: Andre Gafita, MD, Post-doctorate Researcher, Nuclear Medicine, Johns Hopkins University, Baltimore, MD
Written by: Rashid K. Sayyid, MD, MSc – Robotic Urologic Oncology Fellow at The University of Southern California, @rksayyid on Twitter during the 2025 Genitourinary (GU) American Society of Clinical Oncology (ASCO) Annual Meeting, San Francisco, CA, Thurs, Feb 13 – Sat, Feb 15, 2025.