Is 18F-FDG PET needed to assess 177Lu-PSMA Therapy Eligibility? A VISION-like, Single-Center Analysis.

Introduction: 18F-2-Fluoro-2-deoxyglucose (18F-FDG) in addition to Prostate Specific Membrane Antigen (PSMA) PET has been employed to assess the eligibility for PSMA-targeted therapy by some centers. However, it remains unclear, if both examinations are needed as a part of work-up in the clinical practice, or if PSMA-PET alone, as was done in the positive phase 3 VISION trial, is sufficient to identify suitable candidates. The aim was to re-analyze all patients who received both 18F-FDG- and PSMA-PET for PSMA-targeted therapy eligibility assessment using the VISION trial criteria. Methods: Eighty-nine men with mCRPC referred to 177Lu-PSMA therapy from June 2019 until October 2021 who received both 18F-FDG- and PSMA-PET (using either 68Ga-PSMA-11 or 18F-PSMA-1007) examinations within 2 weeks were included in this analysis. Eligibility status was determined in accordance with either (a) knowledge of both 18F-FDG- and PSMA-PET (clinical routine) or (b) VISION criteria with PSMA-PET only (study reassessment, done twice with liver only for PSMA-11 and liver/spleen as reference for PSMA-1007). A metastasis seen on 18F-FDG-PET or CT but not on PSMA-PET was denoted as a mismatch finding and led to exclusion from 177Lu-PSMA therapy. Based on clinical assessment, 52 patients received 177Lu-PSMA therapy, 37 did not; all patients were reassessed. Results: Patients treated with 177Lu-PSMA therapy had significantly longer OS than those not treated (12.4 vs. 6.8 months, p<0.01). PSMA-only analysis (spleen/liver reference) and 18F-FDG/PSMA mismatch reads had a substantial agreement (Cohen`s κ=0.73). 18% (n = 16/89) of patients had a mismatch finding based on 18F-FDG/PSMA-PET. With the liver/spleen reference, a minor fraction of patients who had no mismatch finding (and were therefore treated) would have been withheld from therapy by PSMA-only analysis (3%). 3% (n = 3) of all patients had an 18F-FDG/PSMA mismatch finding not detected by the PSMA-PET only (VISION-like) analysis. For patients not receiving PSMA therapy, the overall survival was not statistically significantly different comparing 18F-FDG/PSMA mismatch vs. non-mismatch (P = 0.61) patients. Conclusion: 18F-FDG- and PSMA-PET provide complementary information, yet less than 5% of patients had mismatch findings not detected using PSMA-PET only. Based on our data, 18F- FDG/PSMA mismatch examination and PSMA-only analysis have a substantial level of agreement.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 2022 Dec 15 [Epub ahead of print]

Robert Seifert, Tugce Telli, Boris Hadaschik, Wolfgang Peter Fendler, Phillip H Kuo, Ken Herrmann

University Hospital Essen, Germany., University of Arizona.