Lesions with a high uptake of 18-fluorodeoxyglucose (F-FDG) on positron emission tomography / computed tomography (PET/CT) can be benign and malignant. New radiotracers, such as the gallium-68 (Ga) labeled fibroblast activation protein inhibitor-4 (FAPI-04), could be used to diagnose colorectal carcinoma. This study aimed to evaluate the efficacy of Ga-FAPI-04 PET in differentiating benign from malignant in F-FDG-avid colorectal lesions.
An azoxymethane/dextran sodium sulfate (AOM/DSS) – induced rat colorectal tumor model was developed. Double tracer Ga-FAPI-04 and F-FDG PET/CT were applied in the rat model and 22 patients. The PET/CT data were analyzed with enteroscopy, histopathological observations, immunohistochemistry (IHC) staining and radioautography results. One hundred seventy-two patients with pathologically confirmed colorectal lesions were enrolled in FAP IHC staining.
We found that Ga-FAPI-04 PET/CT imaging accurately distinguished the malignancy from benign inflammatory lesions in an AOM/DSS-induced rat colorectal tumor model. Eight out of 22 gastric cancer patients without colorectal carcinoma had F-FDG uptake in the colorectum, but Ga-FAPI-04 PET was negative in these sites. An inflammatory lesion or adenoma did not interfere with Ga-FAPI-04 PET imaging. Among the F-FDG-avid colorectal lesions, 85.1% (80 out of 94) of pathologically malignant lesions were FAP-positive, and only 20.5% (16 out of 78) of the premalignant or benign lesions had a week Ga-FAPI-04 uptake.
Ga-FAPI-04 PET/CT could be used to distinguish between benign and malignant in F-FDG-avid colorectal lesions.

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