FDG-Avid But FAPI-Negative Intramucosal Carcinoma in a Colorectal Adenoma

Area of Science:

• Oncology
• Nuclear Medicine
• Gastroenterology

Background:

• Fibroblast activation protein inhibitor (FAPI) PET imaging targets cancer-associated fibroblasts.
• FAPI PET demonstrates high uptake in advanced colorectal cancer.
• The utility of FAPI PET in early colorectal lesions is not well-established.

Purpose of the Study:

• To evaluate the performance of 18F FAPI-74 PET/CT in detecting early colorectal lesions.
• To compare FAPI PET/CT with FDG PET/CT in a patient with a history of hepatocellular carcinoma.

Main Methods:

• A man in his 70s with a history of hepatocellular carcinoma underwent both FDG PET/CT and 18F FAPI-74 PET/CT.
• FDG PET/CT and FAPI PET/CT findings were analyzed for focal uptake in the sigmoid colon.
• Endoscopic resection was performed for histological confirmation.

Main Results:

• FDG PET/CT revealed intense focal uptake in the sigmoid colon.
• 18F FAPI-74 PET/CT demonstrated no abnormal uptake in the sigmoid colon lesion.
• Histopathology confirmed carcinoma in adenoma confined to the lamina propria, lacking a desmoplastic reaction.

Conclusions:

• FAPI uptake correlates with stromal fibroblast activity.
• FAPI PET/CT may have limited sensitivity for detecting intramucosal adenomas with minimal desmoplasia.
• FDG PET/CT may be more suitable for detecting early colorectal lesions with minimal stromal changes.