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Serous cystadenoma of the pancreas is a type of pancreatic cystic neoplasm frequently found in clinical practice. Serous cystadenoma of the pancreas can have a varied morphological presentation on imaging examinations. Therefore, it is sometimes very challenging to differentiate serous cystadenoma of the pancreas from pancreatic malignancy. In this study, we present a case of serous cystadenoma of the pancreas showing focally elevated radiotracer uptake on 68 Ga-FAPI PET/CT. Considering potential future clinical use of 68 Ga-FAPI PET/CT in malignancy, awareness of the false-positive findings is important for the differential diagnosis and management of these lesions.

False-positive findings of mediastinal lymph node often confound the image interpretation of the preoperative PET/CT in non-small cell lung cancer. In this case, we reported 18F-FDG and 68Ga-FAPI PET/CT findings in a patient with squamous cell lung cancer. 18F-FDG-based TNM stage was stage IIIA (T1bN2M0) due to increased uptake in the enlarged right lower paratracheal lymph node. However, no abnormal 68Ga-FAPI uptake was observed in this lymph node. Subsequent histopathological examination revealed no evidence of malignancy in the mediastinal lymph nodes. Therefore, the tumor stage was downstaged to stage IA (T1bN0M0), which was in accordance with 68Ga-FAPI-based TNM stage.

This study aimed to investigate the diagnostic performance of [68Ga]Ga-FAPI PET/CT for primary and metastatic pancreatic carcinoma lesions and compare the results with those of [18F]-fluorodeoxyglucose ([18F]FDG) PET/CT. Patients with suspected or diagnosed pancreatic malignancy, who underwent contemporaneous [18F]FDG and [68Ga]Ga-FAPI PET/CT between June 2020 and January 2021, were retrospectively analyzed. Routine contrast-enhanced CT (CE-CT) is performed in all patients as standardized care. Findings were confirmed by histopathology or radiographic follow-up. We compared radiotracer uptake, diagnostic performance, and TNM (tumor-node-metastasis) classifications. We evaluated 36 participants (25/36 men; median age, 60 years), including 26 patients with pancreatic malignancies and ten patients with pancreatic benign lesions. [68Ga]Ga-FAPI PET/CT showed higher radiotracer uptake and higher sensitivity than [18F]FDG PET/CT in evaluating primary tumors (SUVmax, 21.4 vs. 4.8; sensitivity, 100% vs. 73.1%), involved lymph nodes (SUVmax, 8.6 vs. 2.7; sensitivity, 81.8% vs. 59.1%), and metastases (SUVmax, 7.9 vs. 3.5; sensitivity, 91.5% vs. 44.0%); Compared with [18F]FDG, [68Ga]Ga-FAPI PET/CT upstaged six patients’ TNM staging (6/23, 26.1%) and changed two patients’ clinical management (2/23, 8.7%). Compared with CE-CT, [68Ga]Ga-FAPI PET/CT upgraded TNM staging in five patients (5/23, 21.7%) and changed the therapeutic regimen in only one patient (1/23, 4.3%). Intense [68Ga]Ga-FAPI uptake was observed throughout the pancreas in 12/26 pancreatic malignancies; dual-time point [68Ga]Ga-FAPI PET/CT may differentiate pancreatitis from malignancy. Compared with [18F]FDG PET/CT, [68Ga]Ga-FAPI PET/CT shows higher sensitivity in detecting primary pancreatic tumors, involved lymph nodes, and metastases and is superior in terms of TNM staging. Prospective trials with larger patient population are needed to evaluate whether [68Ga]Ga-FAPI PET/CT could elicit treatment modification in pancreatic cancer when compared with standard of care imaging.

Metastases to gastrointestinal tract from breast cancer are very rare and can be diagnostically challenging. In this case, we reported 18 F-FDG and 68 Ga-FAPI PET/CT findings in a 54-year-old women with such uncommon metastases from breast cancer. Although the primary tumor of breast cancer remained radiologically occult, 68 Ga-FAPI PET/CT showed a far better tumor-to-background ratio than 18 F-FDG PET/CT for detecting the metastatic lesions, especially for detecting the retroperitoneal lymph node and rectal metastases.

68 Ga-labeled PET tracer targeting PSMA is a promising diagnostic approach for staging and restating of prostate cancer (PCa), but cases with clinically relevant PCa and false-negative PSMA PET/CT have been reported. In this case, we reported 68 Ga-PSMA, 18 F-FDG, and 68 Ga-FAPI PET/CT findings in a 65-year-old man with de novo metastatic PCa. 68 Ga-FAPI PET/CT detected non-PSMA/FDG-avid primary PCa, consisting with multiparametric MRI findings. The subsequent histopathologic examination confirmed a Gleason 4 + 5 PCa. This case highlighted that 68 Ga-FAPI PET/CT may be a useful imaging modality for primary PCa detection and localization.

A 55-year-old woman with endogenous hyperinsulinemia hypoglycemia was clinically diagnosed with insulinoma. Contrast-enhanced MRI revealed an inconclusive hypointense lesion in the pancreatic tail, and the enhancement pattern does not support the diagnosis of insulinoma. 68Ga-DOTATATE PET/CT showed intense radioactivity in this nodule, similar to the radioactivity of the adjacent spleen. Therefore, the diagnosis of accessory spleen cannot be excluded. Follow-up with 68Ga-exendin-4 PET/CT also showed intense uptake in this nodule, but no significant uptake in the spleen was observed at this time. Therefore, the insulinoma was unmasked from the spleen, excluding the diagnosis of accessory spleen, and allowing curative surgery.

Primary pulmonary lymphoepithelioma-like carcinomas (LELCs) are extremely rare tumors with better prognosis than other types of lung malignancies. In this case, we present 18F-FDG and 68Ga-DOTATATE PET/CT findings in a 52-year-old woman with pathologically confirmed pulmonary LELC. The pulmonary LELC presented mild 18F-FDG but avid 68Ga-DOTATATE uptake, indicating that the somatostatin receptor 2 may be highly expressed in LELCs. Therefore, 68Ga-DOTATATE PET/CT is a useful tool for tumor detection and initial staging in patients with LELCs.

Ankylosing spondylitis represents an inflammatory arthropathy with a predilection for the axial skeleton. We reported 68Ga-FAPI PET/CT finding of ankylosing spondylitis in a 65-year-old patient with rectal cancer. In addition to accumulating in primary tumor and metastatic lymph nodes, increased 68Ga-FAPI uptake was also observed in the sacroiliac and costovertebral joints, indicating sacroiliitis and spondylitis. However, no abnormal 18F-FDG uptake was observed in the inflammatory lesions. This case highlighted that 68Ga-FAPI PET/CT is useful for the evaluation of inflammatory conditions in ankylosing spondylitis.

18F-FDG PET/CT was performed to locate the primary lesion in a 71-year-old man with bone metastasis. However, no abnormal 18F-FDG activity likely presenting the primary tumor was observed. 68Ga-fibroblast activation protein inhibitor PET/CT was then performed for further detecting the primary tumor, which showed a higher activity in lesions of bone metastases than 18F-FDG. Additionally, another lesion with intense uptake was observed in the inferior pole of right kidney, likely presenting the primary tumor. A renal biopsy revealed the diagnosis of chromophobe renal cell carcinoma. This case highlighted that 68Ga-fibroblast activation protein inhibitor could be a promising radiopharmaceutical in the diagnosis of renal cell carcinoma.

Accurate clinical staging is crucial for managing nasopharyngeal carcinoma (NPC). However, false-positive finding of cervical lymph nodes in 18F-FDG PET/CT and MRI may lead to unnecessary chemotherapy for NPC. In this case, we report a patient with NPC who was incorrectly diagnosed with bilateral cervical lymph node metastases by both 18F-FDG PET/CT and MRI. Subsequent pathology results showed proliferating lymphoid cells with no signs of tumor metastasis. Interestingly, no abnormal 68Ga-FAPI uptake was observed in the nonmetastatic reactive lymph nodes. Therefore, 68Ga-FAPI PET/CT may be useful for assessment of pretreatment lymph node status in NPC.

The present study compared Ga-FAPI and F-FDG PET/CT in a patient with cholangiocellular carcinoma. In this case, Ga-FAPI PET shows much higher tumor-to-background contrast of primary tumor and reveals more metastatic lesions, especially the micrometastases of bones, than F-FDG PET.