Increased 18 F-FAPI uptake in bones and joints of lung cancer patients: characteristics and distributions

Objective This study investigated the distribution and characteristics of various bone and joint lesions on 18 F-FAPI PET/CT in lung cancer patients. Methods Seventy-four lung cancer patients who underwent 18 F-FAPI PET/CT were reviewed. Bone and joint lesions with elevated 18 F-FAPI uptake were recorded and analyzed. The distribution and maximum uptake value (SUV max ) of different benign lesions or bone metastases were presented. In addition, the SUV max of bone metastases on 18 F-FDG and 18 F-FAPI-04 PET/CT were also compared. Results In 53 patients, a total of 262 lesions presented 18 F-FAPI accumulation. Bone metastases were mainly in vertebrae, pelvis, and ribs, while benign lesions were in vertebral margins, alveolar bone, and shoulder joints. The SUV max of bone metastases was significantly higher than that of benign lesions ( 6.6± 2.8 vs. 4.3± 1.6 , P<0.001 ), with NSCLC cases having higher SUV max values than SCLC cases ( 7.3± 2.7 vs. 3.7± 1.1 , P<0.001 ). Among benign lesions, arthritis and periodontitis demonstrated higher SUV max than degenerative lesions (arthritis: 5.2± 2.3 ; periodontitis: 4.8± 1.5 ; degenerative diseases: 3.6± 0.9 ; P<0.01 and P<0.05 , respectively). The SUV max of bone metastases was comparable between 18 F-FDG and 18 F-FAPI PET/CT. However, 18 F-FAPI PET/CT was found to be superior in identifying cranial metastases compared to 18 F-FDG PET/CT (TBR met/brain : 54.2± 13.5 vs. 0.6± 0.2 , P=0.02 ). Conclusion This study demonstrated that 18 F-FAPI PET/CT is a valuable imaging modality for detecting bone and joint lesions in lung cancer patients. The SUV max of malignant lesions was higher than that of benign lesions, but cannot accurately distinguish benign and malignant lesions. The uptake of FAPI differs among lesions with different pathological types.