1823P - The impact of baseline PSMA PET/CT vs. CT on outcomes of Radium-223 therapy in mCRPC patients

Background

Imaging prior to Radium-223 therapy (Ra-223) is crucial for selecting metastatic castration-resistant prostate cancer (mCRPC) patients with bone-only disease. The purpose of this study was to evaluate if baseline PSMA PET/CT versus CT is associated with biochemical response during Ra-223.

Methods

A secondary analysis of the data of a prospective observational study (NCT04995614) was performed. Patients received a maximum of six cycles of Ra-223 and were retrospectively divided into the PSMA PET/CT (bPSMA) or CT (bCT) group based on baseline imaging technique. All patients received baseline bone scintigraphy. Primary endpoints were alkaline phosphatase (ALP) and prostate specific antigen (PSA) response, defined as ≥ 30% decline from baseline. Secondary endpoints were overall survival (OS) and radiological response.

Results

Between 2017 and 2020, 122 mCRPC patients were included: 18 (14.8%) in the bPSMA and 104 (85.2%) in the bCT group. All baseline characteristics were comparable. No significant differences in ALP or PSA response were found between the groups. The bCT group showed a significant shorter OS compared to the bPSMA group (12.4 vs.19.9 months, p < 0.01, table). Post-therapy soft tissue involvement (STI) was detected in 29/76 patients (38.2%) that received bCT and post-therapy CT (bCT/pCT), compared to 0/18 bPSMA patients. No significant difference in OS was found between bCT/pCT patients without STI and bPSMA patients. Table: 1823P

OS (months) among subgroups

Abbreviations: W/o, without; NR, not reached.

Conclusions

bPSMA versus bCT does not seem to predict biochemical response during Ra-223. Nevertheless, patients in the bCT group had a significantly shorter OS, most likely due to underdetection of STI in this group. Therefore, replacing baseline CT with PSMA PET/CT appears to be a valuable screening method to ensure in-label use of Ra-223.

Clinical trial identification

NCT04995614.

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Bayer.

Disclosure

D. Bosch: Financial Interests, Personal, Invited Speaker: MSD AstraZeneca. W.J.G. Oyen: Financial Interests, Personal and Institutional, Speaker, Consultant, Advisor: Bayer, AAA Novartis. D.M. Somford: Financial Interests, Personal, Advisory Board: Janssen Pharmaceuticals, Bayer, Astellas; Financial Interests, Institutional, Research Grant: Astellas. R. Hermsen: Financial Interests, Personal, Advisory Board: Bayer; Financial Interests, Personal, Other, Personal fees and travel expenses: Bayer. N. Mehra: Financial Interests, Personal and Institutional, Advisory Board, And personal fees and research funding: Bayer; Financial Interests, Personal, Advisory Board: BMS; Financial Interests, Personal and Institutional, Advisory Board, And research grants and personal fees: Roche, Merck Sharp and Dohme; Financial Interests, Personal and Institutional, Advisory Board, And research grants, research funding and personal fees: Astellas, Janssen Pharmaceuticals; Financial Interests, Personal and Institutional, Other, Research grants and personal fees: AstraZeneca, Sanofi; Financial Interests, Institutional, Research Grant: Pfizer, Genzyme. W.R. Gerritsen: Financial Interests, Personal, Advisory Board: BMS, Sanofi Gemzyme, Amgen, Morphosys and CureVac; Financial Interests, Personal and Institutional, Advisory Board, Plus research funding: Astellas, Janssen Pharmaceuticals; Financial Interests, Personal and Institutional, Advisory Board, Plus research funding and speaker fees: Bayer; Financial Interests, Personal, Invited Speaker: MSD. M.J. van der Doelen: Financial Interests, Institutional, Research Grant: Bayer, Janssen Pharmaceuticals; Financial Interests, Personal, Other, Speaker fees: Astellas. I.M. van Oort: Financial Interests, Personal and Institutional, Advisory Board, Plus research funding: MSD/AstraZeneca; Financial Interests, Personal and Institutional, Research Grant, Plus research funding and personal fees: Astellas, Bayer; Financial Interests, Personal and Institutional, Research Grant, Plus personal fees: Janssen Pharmaceuticals; Financial Interests, Personal and Institutional, Research Funding: Pfizer; Financial Interests, Institutional, Research Funding: AAA Novartis. All other authors have declared no conflicts of interest.