⁶⁸Ga-FAPI-04 Positron Emission Tomography Distinguishes Malignancy From ¹⁸F-FDG-Avid Colorectal Lesions

Lesions with a high uptake of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) on positron emission tomography-computed tomography (PET-CT) can be benign and malignant. New radiotracers, such as the gallium 68 (⁶⁸Ga)-labeled fibroblast activation protein inhibitor 4 (FAPI-04), could be used to diagnose colorectal carcinoma. This study aimed to evaluate the efficacy of ⁶⁸Ga-FAPI-04 PET in differentiating benign from malignant ¹⁸F-FDG-avid colorectal lesions.

An azoxymethane/dextran sodium sulfate (AOM/DSS)-induced rat colorectal tumor model was developed. Double-tracer ⁶⁸Ga-FAPI-04 and ¹⁸F-FDG PET-CT were applied in the rat model and 22 patients. The PET-CT data were analyzed with enteroscopy, histopathologic 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 ⁶⁸Ga-FAPI-04 PET-CT imaging accurately distinguished the malignant from benign inflammatory lesions in an AOM/DSS-induced rat colorectal tumor model. Of 22 patients with gastric cancer but without colorectal carcinoma, 8 had ¹⁸F-FDG uptake in the colorectum, but ⁶⁸Ga-FAPI-04 PET was negative in these sites. An inflammatory lesion or adenoma did not interfere with ⁶⁸Ga-FAPI-04 PET imaging. Among the ¹⁸F-FDG-avid colorectal lesions, 80 of 94 pathologically malignant lesions (85.1%) were FAP-positive, and only 16 of the 78 premalignant or benign lesions (20.5%) had a weak ⁶⁸Ga-FAPI-04 uptake.

⁶⁸Ga-FAPI-04 PET-CT could be used to distinguish between benign and malignant ¹⁸F-FDG-avid colorectal lesions.