Prognostic significance of 68Ga-FAPI-PET/CT in patients with bone metastases in various cancers

Abstract Objective:This study aimed to compare and¹⁸FDGPET/CT in patients who develop bone metastases due to various cancers and to investigate the prognostic significance of the ⁶⁸FAPI-PET/CT SUVmax value for survival. Methods:Patients with bone metastases who underwent both ⁶⁸Ga-FAPI PET/CTand¹⁸FDGPET/CT within a 1-week period were included in this retrospective study. The effect of the SUVmax value of bone lesions on overall survival was analyzed. Results:A total of 75 eligible patients with 139 bone lesions were included in this study. The median age of the patients was 55(30–83) and 48 patients (64%) were newly diagnosed. The primary lesion median ⁶⁸Ga-FAPI PET/CT SUVmax value was higher than the median ¹⁸FDGPET/CT SUVmax (10.75 versus 6.7). Bone lesions ⁶⁸Ga-FAPI PET/CT SUVmax median(IQR) were 7.8(4.6–13.2), and ¹⁸FDGPET/CT SUVmax of bone lesions were 5.9(3.8–8.2). More bone lesions were detected on ⁶⁸Ga-FAPI PET/CT than on ¹⁸FDGPET/CT(median IQR 4 [1–9] versus 2 [1–6](p=0.014). The extra lesions observed on ⁶⁸Ga-FAPI PET/CT were mostly sclerotic bone lesions(p = 0.001).⁶⁸Ga-FAPI PET/CT SUVmax was significantly higher in vertebra and thorax lesions(p=0.011 and p=0.018, respectively). While the bone lesion ⁶⁸Ga-FAPI PET/CT SUVmax affected the OS, the ¹⁸FDGPET/CT SUVmax value did not affect the OS (p<0.001 and p=0.079, respectively). In ROC analysis, a cut-off value of ⁶⁸Ga-FAPI PET/CT SUVmax >7.7 was found for OS(AUC:0.619). The median OS in the group above the cut-off value was worse than that in the group below the cut-off value (32 versus 45) months (p=0.002). In the multivariate analysis for OS, the ⁶⁸Ga-FAPI PET/CT SUVmax of bone lesions was an important parameter,as well as cancer subtype, ALP level, and disease occurrence. Conclusions:⁶⁸Ga-FAPI PET/CT detected more bone lesions and higher SUVmax values than ¹⁸FDGPET/CT in various cancers. The prognostic value of the SUVmax value of ⁶⁸Ga-FAPI PET/CT bone lesions was observed regardless of disease subtype.