DP115 | PROSPECTIVE COMPARISON OF 18F-FDG-PET/CT AND 68GA-PSMA-PET/CT FOR STAGING OF NEWLY DIAGNOSED MULTIPLE MYELOMA

Background: ¹⁸F-FDG-PET/CT is the most used technique to detect bone disease in multiple myeloma (MM) and is recommended for response assessment. Prostate specific membrane antigen (PSMA) is overexpressed in tumors with neoangiogenesis, including MM. Aims and Methods: We present a prospective single-center study aimed at evaluating diagnostic performance of PSMA-PET in MM through comparison to FDG-PET. Patients (pts) with newly diagnosed (ND)MM underwent both scans within 14 days before start of any treatment. The scans were compared in terms of n°of focal lesions (FLs), paraskeletal disease (PSD), diffuse bone marrow (BM) uptake and SUV_max. Results: 51 pts were enrolled. In terms of positivity/negativity, 40 pts(78%) had concordant scans: 23(45%) were positive (pos) and 17(33%) negative (neg). Among discordant pts(22%), 9(18%) had pos FDG and 2(4%) had pos PSMA(k=0.57). FLs were detected in 27 pts(53%): FDG-PET detected FLs in 26(51%) with 7(14%) having neg PSMA; PSMA-PET detected FLs in 20(39%) with 1(2%) having neg FDG. In 8 pts(16%) FDG and PSMA-PET detected the same n°of FLs; in 13(25%) and 6 pts(12%) FDG and PSMA revealed a higher n°of FLs than the other tracer respectively (p=0.09). Median SUV_max of FLs was 5.7 for FDG and 5.2 for PSMA. 1 pt had PSMA uptake in FLs resulting higher than physiologic liver uptake (reference for radioligand therapy indication). PSD lesions were detected in 10 pts(20%) by FDG-PET and in 9 pts(18%) by PSMA-PET. Median SUV_max of PSD was 5.5 for FDG and 4.7 for PSMA. 2 pts had PSMA uptake in PSD lesions resulting higher than liver. Regarding BM diffuse uptake, 36 pts(71%) had concordant scans: 5(10%) were pos and 31(61%) were neg by both tracers. Among discordant pts, 12(23%) had pos FDG and 3(6%) had pos PSMA-PET(k = 0.24). Median SUV_max of BM was 4.8 for FDG and 3.3 for PSMA. Conclusion: According to our results, in NDMM pts FDG-PET features a positivity rate resulting higher in detecting FLs and BM diffuse uptake and similar in detecting PSD lesions as compared to PSMA-PET. PSMA uptake of FLs and/or PSD lesions had higher values than physiologic liver uptake only in 2 pts. Due to these observations, lack of standardization in response assessment, short half-life requiring local cyclotron for on-site production and high costs, PSMA does not seem optimal for imaging or theranostics in NDMM pts. It is not excluded that PSMA uptake may be higher in advanced phases of MM, characterized by further increase of neoangiogenesis.