Semiquantitative muscle parameters derived from FAPI and FDG PET/CT in evaluating sarcopenia among patients with malignant tumors

BACKGROUND: The objective of this study is to explore and compare the potential utility of fibroblast activation protein inhibitor (FAPI) and fluorodeoxyglucose PET/computed tomography (CT) in assessing sarcopenia among patients with malignant tumors. METHODS: A retrospective analysis was conducted on 127 patients with histologically confirmed malignant tumors who underwent both 18 F/ 68 Ga-FAPI and fluorine-18-fluorodeoxyglucose ( 18 F-FDG) PET/CT scans. Clinical characteristics and PET/CT parameters of maximum and mean standard uptake value (SUV max and SUV mean ) of muscle at the 3 rd lumbar (L3) level were reviewed. Skeletal muscle area at the L3 level was measured, and skeletal muscle index was calculated to determine sarcopenia. The association between sarcopenia and PET/CT parameters was analyzed. RESULTS: The incidence of sarcopenia was 41.7% among these 127 patients. Higher age, male, lower BMI, lower SUV max and SUV mean of muscle from 18 F/ 68 Ga-FAPI PET/CT, and lower SUV max of muscle from 18 F-FDG PET/CT were correlated with a higher prevalence of sarcopenia ( P < 0.05). Besides, no significant differences in SUV max and SUV mean of muscle were noted between 18 F-FAPI and 68 Ga-FAPI groups. The best cutoff value of SUV max of muscle from 18 F/ 68 Ga-FAPI PET/CT was 1.17, yielding the area under the curve (AUC) of 0.764 and sensitivity and specificity of 74.3% and 71.7%, while the optimal cutoff value of SUV max of muscle from 18 F-FDG PET/CT was 0.76, with an AUC of 0.642 and sensitivity and specificity of 36.5% and 86.8%, respectively. CONCLUSION: Patients with sarcopenia exhibit decreased muscle uptake of FAPI and fluorodeoxyglucose. FAPI PET/CT emerges as a more valuable tool for sarcopenia assessment in patients with malignant tumors compared to fluorodeoxyglucose PET/CT.