68Ga-FAPI improves tumor staging in patients with colorectal cancer: comparing to 18F-FDG PET/CT

Abstract

Purpose Gallium-68 (68Ga)-labeled fibroblast-activation protein inhibitor (FAPI) is a novel tracer that binds fibroblast-activation protein (FAP), which is overexpressed in colorectal cancers with a prominent stroma including cancer-associated fibroblasts (CAFs). The present study aimed to compare the diagnostic performance of 68Ga-FAPI positron emission tomography (PET)/computed tomography (CT) with that of fluorine-18 (18F)-fluorodeoxyglucose (FDG) PET/CT in primary and metastatic colorectal cancer lesions. Methods This prospective study included the image analyses of 37 patients with colorectal cancer who were sequentially evaluated using PET/CT with 18F-FDG and 68Ga-FAPI. Tracer uptakes were compared using Wilcoxon’s signed-rank test. Results The cohort comprised 37 patients, including 18 treatment-naïve patients and 19 post-treatment patients. In primary colorectal cancer lesions, the average 68Ga-FAPI and 18F-FDG maximum standardized uptake values (SUVmax) were 12.5 ± 4.8 and 13.2 ± 5.7 (P = 0.38), respectively, in the treatment-naïve group and 6.0 ± 4.3 and 7.9 ± 7.2, respectively, in the neoadjuvant chemotherapy group (P = 0.09); the detection rate was 100% with both tracers (18/18). The SUVmax value of 68Ga-FAPI in signet-ring/mucinous carcinomas (12.3 ± 5.2) was higher than that of 18F-FDG (8.3 ± 4.0) (P = 0.03). In addition, the average 68Ga-FAPI uptake was lower than that of 18F-FDG in poorly differentiated carcinomas (12.7 ± 3.7 vs. 18.1 ± 4.1, P = 0.04). Compared with 18F-FDG PET/CT, clinical TNM staging based on 68Ga-FAPI PET/CT led to upstaging in 6 patients (16.2%) and downstaging in 3 patients (8.1%). In peritoneal and liver metastases, both the SUVmax and the target/background ratio were higher with 68Ga-FAPI compared to 18F-FDG (3.7 vs. 2.6, P = 0.02, and 6.5 vs. 0.89, P = 0.01, respectively). Conclusion As a novel PET/CT tracer, 68Ga-FAPI showed its advantage in the detection of lymph nodes, and distant metastases, which improved staging of CRC.