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

Abstract

18F-FDG and prostate-specific membrane antigen (PSMA) PET have been used to assess eligibility for PSMA-targeted therapy by some centers. However, it remains unclear whether both examinations are needed as a part of workup in the clinical practice or whether PSMA PET alone, as was done in the positive phase 3 VISION trial, is sufficient to identify suitable candidates. The aim was to reanalyze all patients who underwent both 18F-FDG and PSMA PET for PSMA-targeted therapy eligibility assessment using the VISION trial criteria. Methods: Eighty-nine men with metastatic castration-resistant prostate cancer referred to 177Lu-PSMA therapy from June 2019 to October 2021 who underwent both 18F-FDG and PSMA PET (using either 68Ga-PSMA-11 or 18F-PSMA-1007) examinations within 2 wk were included in this analysis. Eligibility status was determined in accordance with either knowledge of both 18F-FDG and PSMA PET (clinical routine) or 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. On the basis of clinical assessment, 52 patients received 177Lu-PSMA therapy, and 37 did not; all patients were reassessed. Results: Patients treated with 177Lu-PSMA therapy had significantly longer overall survival than those not treated (12.4 vs. 6.8 mo, P < 0.01). PSMA-only analysis (spleen/liver reference) and 18F-FDG/PSMA mismatch reads had substantial agreement (Cohen κ = 0.73). Eighteen percent (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%). Three percent (n = 3) of all patients had an 18F-FDG/PSMA mismatch finding not detected by 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 versus nonmismatch (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.