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Objective In this study, we aimed to evaluate the diagnostic sensitivities of 68 Ga-FAPI-04 PET/CT and 18 F-FDG PET/CT in the primary tumor, and nodal, peritoneal and distant organ metastases of primary and recurrent gastric adenocarcinoma (GAc) with patient and lesionbased comparison. Materials and methodTwenty-one patients with histopathologically proven newly diagnosed or recurrent GAc who underwent 18 F-FDG and 68 Ga-FAPI-04 imaging were included in the study. Both imaging techniques were evaluated visually according to the intensity of organbased uptake. SUVmax and tumor-to-background ratio (TBR) values obtained from primary tumor/relapse and metastatic organs were compared statistically.Results 68 Ga-FAPI-04 uptake was positive in all 15 newly diagnosed patients, while two patients among them who had mucinous and signet ring cell carcinoma did not exhibit 18 F-FDG uptake. The sensitivity and specificity of 68 Ga-FAPI-04 PET/CT in detecting primary gastric were 100%, while the sensitivity and specificity of 18 F-FDG were 86.6 and 100%, respectively. 68 Ga-FAPI-04 imaging revealed diffuse stomach uptake in seven patients, while 18 F-FDG could only show two of them. The sensitivity and specificity of in-patient-based detection of lymph node metastases were 100 and 95.2%, respectively, while these values were 71.4 and 93.7%, respectively, for 18 F-FDG. For peritoneal involvement 68 Ga-FAPI-04 had a sensitivity and specificity of 100%, whereas 18 F-FDG had a sensitivity of 40% and a specificity of 100%.Conclusion 68 Ga-FAPI-04 PET/CT is an imaging modality with the potential of yielding more sensitive and specific findings 18 F-FDG PET/CT. This modality may help avoid invasive diagnostic procedures that may be frequently required in GAc.

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68Ga-FAPI (fibroblast activation protein-specific inhibitor) PET/CT was performed in a 56-year-old man with multiple liver masses, which were confirmed grade 2 well-differentiated neuroendocrine tumors with liver Tru-Cut biopsy. With 68Ga-DOTATE PET/CT, primary tumor in the pancreas, multiple metastases in the liver and metastatic portocaval lymph node were detected. In 68Ga-FAPI PET/CT imaging performed for comparison, it was seen that metastatic lesions in the liver were distinguished much better because of low background activity, and the primary tumor and metastatic lymph node were clearly selected. This case suggested that FAPI-bounded radionuclides may be useful in the evaluation and targeted therapy of neuroendocrine tumors.