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

Objective This study aimed to compare (18)FDGPET/CT in patients who develop bone metastases due to various cancers and to investigate the prognostic significance of the (68)FAPI-PET/CT SUVmax value for survival. Methods Patients with bone metastases who underwent both (68) Ga-FAPI PET/CT and (18)FDGPET/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(64%) patients were newly diagnosed. The primary lesion median (68) Ga-FAPI PET/CT SUVmax value was higher than the median (18)FDGPET/CT SUVmax (10.75 versus 6.7). Bone lesions (68) Ga-FAPI PET/CT SUVmax median (IQR) were 7.8 (4.6-13.2), and (18)FDGPET/CT SUVmax of bone lesions were 5.9 (3.8-8.2). More bone lesions were detected on (68) Ga-FAPI PET/CT than on (18)FDGPET/CT(median IQR 4 [1-9] versus 2 [1-6] (p = 0.014). The extra lesions observed on (68) Ga-FAPI PET/CT were mostly sclerotic bone lesions (p = 0.001).(68) Ga-FAPI PET/CT SUVmax was significantly higher in vertebra and thorax lesions (p = 0.011 and p = 0.018, respectively). While the bone lesion (68) Ga-FAPI PET/CT SUVmax affected the OS, the (18)FDGPET/CT SUVmax value did not affect the OS (p < 0.001 and p = 0.079, respectively). In ROC analysis, a cut-off-off value of (68) Ga-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 (68) Ga-FAPI PET/CT SUVmax of bone lesions was an important parameter, as well as cancer subtype, ALP level, and disease occurrence. Conclusions (68) Ga-FAPI PET/CT detected more bone lesions and higher SUVmax values than (18)FDGPET/CT in various cancers. The prognostic value of the SUVmax value of (68) Ga-FAPI PET/CT bone lesions was observed regardless of disease subtype.