18F-FAPI-04 PET/CT Reveals Thoracic Duct Tumor Infiltration Secondary to Gastric Cancer

Area of Science:

• Oncology
• Nuclear Medicine
• Radiology

Background:

• Gastric adenocarcinoma staging relies on accurate assessment of tumor burden and lymphatic spread.
• ¹⁸F-FDG PET/CT is standard for staging but may miss subtle metastatic disease.
• Fibroblast activation protein (FAP) targeted imaging offers potential for improved detection of tumor-associated processes.

Purpose of the Study:

• To report the utility of ¹⁸F-FAPI-04 PET/CT in identifying thoracic duct infiltration in advanced gastric cancer.
• To compare the sensitivity of ¹⁸F-FAPI-04 PET/CT versus ¹⁸F-FDG PET/CT for detecting lymphatic spread.

Main Methods:

• A 61-year-old man with advanced gastric adenocarcinoma underwent both ¹⁸F-FDG PET/CT and ¹⁸F-FAPI-04 PET/CT.
• ¹⁸F-FAPI-04 PET/CT was performed as an exploratory imaging study.
• Findings were analyzed for primary tumor size, nodal metastases, and specific lesions suggestive of lymphatic involvement.

Main Results:

• ¹⁸F-FAPI-04 PET/CT revealed a larger primary tumor and more extensive nodal metastases compared to ¹⁸F-FDG PET/CT.
• Intense ¹⁸F-FAPI-04 uptake was observed in a subtle linear lesion along the left posterior mediastinum, consistent with thoracic duct involvement.
• This thoracic duct lesion showed unremarkable uptake on ¹⁸F-FDG PET/CT and CT morphology.

Conclusions:

• ¹⁸F-FAPI-04 PET/CT demonstrates superior sensitivity in detecting occult lymphatic spread, including thoracic duct infiltration, in advanced gastric cancer.
• This finding, though lacking histopathological confirmation, suggests FAPI-based imaging may enhance staging accuracy.
• FAPI PET/CT may represent a valuable tool for identifying previously undetected metastatic pathways in gastric adenocarcinoma.