(UroToday.com) The 37th Annual European Association of Urology Congress held in Amsterdam, Netherlands between July 1st, and 4th 2022 was host to an abstract session regarding improvements in metastatic prostate cancer with a focus on imaging and treatment. Dr. Andrei Gafita presented a novel framework for treatment response evaluation using prostate-specific membrane antigen (PSMA)-PET/CT in patients with metastatic prostate cancer (RECIP 1.0).
PSMA-PET/CT is a novel imaging technique for staging of prostate cancer. While PSMA-PET/CT has gained significant popularity in the pre-treatment high risk and biochemical recurrence disease spaces, there is limited evidence regarding the prognostic utility of PSMA PET/CT for response assessment in men with advanced prostate cancer, and no standardized criteria for response evaluation using PSMA-PET/CT has been developed/validated yet.
The objectives of this study were to develop a novel framework for Response Evaluation Criteria in PSMA-PET/CT (RECIP) 1.0 and a composite response classification, which combines responses by serum PSA measurement and RECIP 1.0 (PSA+RECIP).
This study was an international, multicenter retrospective analysis of 124 men with mCRPC who received 177Lu-PSMA radioligand therapy. These patients underwent PSMA-PET/CT at baseline and at 12 weeks post-treatment. Pairs of baseline and 12 weeks imaging were interpreted by three blinded readers for appearance of new lesions via a consensus. Tumor lesions were segmented using qPSMA software and the total PSMA-positive tumor volume (PSMA-VOL) was obtained.
RECIP 1.0 was developed using the appearance of new lesions and changes in PSMA-VOL:
- Complete response (RECIP-CR): Absence of any PSMA-ligand uptake on interval PET
- Partial response (RECIP-PR): Decline ≥30% in PSMA-VOL and no appearance of new lesions
- Progressive disease (RECIP-PD): Increase ≥20% in PSMA-VOL and appearance of new lesions)
- Stable disease (RECIP-SD): Any condition but RECIP-PR or RECIP-PD
PSA level changes at 12 weeks by the prostate cancer working group-3 (PCWG3) criteria were recorded. Responses by PSA+RECIP were defined as follows:
- Response: PSA decline ≥50% or RECIP-PR/CR
- Progression: PSA increase ≥25% or RECIP-PD
The study outcomes were:
- Primary: Prognostic value of RECIP 1.0 for overall survival
- Secondary: Prognostic accuracy (C-index) of PSA+RECIP versus PSA responses.
The documented RECIP responses were as follows:
- RECIP-CR: 0 (0.0%)
- RECIPE-PR: 38 (30.6%)
- RECIP-PD: 39 (31.5%)
- RECIP-SD: 47 (37.9%)
Median OS by RECIP response was significantly lower in the RECIP-PD group (median OS of 8.3 months), compared to those with stable disease (median OS 13.1 months) or a partial response (RECIP-PR: 21.7 months, p<0.001). PSA+RECIP had superior C-indices in identifying responders and progressors compared to PSA alone: 0.65 vs 0.62 (p=0.028) and 0.66 vs 0.63 (p=0.044), respectively.
The authors concluded as follows:
- PSMA-PET/CT by RECIP 1.0 is prognostic for overall survival and can be used as a response biomarker to monitor early efficacy of 177Lu-PSMA in men with mCRPC.
- PSA+RECIP may be used as a novel composite endpoint in mCRPC clinical trial design.
- These findings warrant validation in a prospective setting.
Presented by: Dr. Andrei Gafita, MD, Ahmanson Translational Theranostics Division, 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 2022 European Association of Urology (EAU) Annual Hybrid Meeting, Amsterdam, NL, Fri, July 1 – Mon, July 4, 2022.