Gastrointestinal cancer with indeterminate 18F-FDG PET/CT findings: Diagnostic efficacy analysis of 68Ga-FAPI-04 PET/MRI.

Abstract

The present prospective study aimed to investigate whether gallium-68-labeled fibroblast activation protein inhibitor-04 (⁶⁸Ga-FAPI-04) positron emission tomography (PET)/magnetic resonance imaging (MRI) could provide notably increased diagnostic accuracy, semi-quantitative parameters, staging capability, diagnostic guidance value and improved clinical benefits compared with fluorine-18-labeled fluorodeoxyglucose (¹⁸F-FDG) PET/computed tomography (CT) in gastrointestinal (GI) cancer with atypical metabolic activity (uncertain ¹⁸F-FDG imaging results). In total, 22 patients with histopathologically confirmed GI cancer, clinically suspected of recurrence or metastasis, but with atypical/inconclusive ¹⁸F-FDG PET/CT results, were analyzed. The present study planned to perform ⁶⁸Ga-FAPI-04 PET/MRI within 1-4 days. The diagnostic performance of both tracers was evaluated. Tumor-to-background ratio was used to quantify the radiotracer uptake. The present study employed Fisher's exact test to statistically analyze the association between pathological subtypes and changes in tumor staging, as well as treatment decisions indicated by ⁶⁸Ga-FAPI-04 PET. The results demonstrated that ⁶⁸Ga-FAPI-04 had significantly higher sensitivity compared with ¹⁸F-FDG in detecting lymph node involvement (100 vs. 89.01%; P=0.001) and distant organ metastases (92.31 vs. 61.54%; P=0.008). Me ⁶⁸Ga-FAPI-04 uptake was significantly higher in primary tumors [median, 6.13 (range, 5.71-7.57) vs. 2.62 (1.82-3.03); P=0.004], lymph nodes (9.07±2.93 vs. 3.96±1.73; P<0.001) and various metastatic sites (3.31±2.19 vs. 6.87±4.16; P<0.001). The findings indicated that ⁶⁸Ga-FAPI-04 has potential advantages in diagnostic efficiency and visual evaluation. Furthermore, ⁶⁸Ga-FAPI-04 altered staging in 36.4% (8/22) of patients and refined the treatment strategies for 27.3% (6/22), particularly those with poorly differentiated adenocarcinoma or mucinous carcinoma. For the 22 patients in the present study, the hospital cost for ⁶⁸Ga-FAPI-04 PET/MRI was higher compared with that for ¹⁸F-FDG PET/CT. However, it generated overall benefits that essentially offset the additional costs. By enabling the timely detection of anastomotic recurrence, lymph node metastasis and distant metastasis for prompt intervention, it saved time, reduced the risk of further disease progression, and also minimized some unnecessary medical procedures caused by false-positive ¹⁸F-FDG results. These findings suggested that ⁶⁸Ga-FAPI-04 PET/MRI is key to enhancing the diagnostic performance for ¹⁸F-FDG metabolically atypical GI tumors, refining clinical decision-making and providing economic benefits. This clinical trial was registered at Clinicaltrials.gov with ID NCT06270394 (date of registration, February 20th, 2024; retrospectively registered).