68Ga-FAPI-04 PET for surveillance of anastomotic recurrence in postoperative patients with gastrointestinal cancer: a comparative study with 18F-FDG PET

Abstract Purpose: 68Ga-FAPI-04 PET imaging has shown clinical advantages for detecting and staging various solid tumor types, including gastrointestinal cancer. This study aims to compare the diagnostic efficacy of 68Ga-FAPI-04 PET and 18F-FDG PET for detecting anastomotic recurrence in postoperative patients with gastrointestinal cancer and to characterize the pattern of 68Ga-FAPI-04 uptake at surgical wounds post-surgery. Methods: This study involved 63 gastrointestinal cancer patients who underwent 68Ga-FAPI-04 and 18F-FDG PET/CT imaging, or 68Ga-FAPI-04 PET/CT imaging only for postoperative surveillance after curative surgical resection. The SUVmax at surgical wounds (anastomotic sites and abdominal incision sites) and its corresponding ratio compared to background were assessed. Endoscopic pathology confirmed anastomotic recurrence or it was ruled out by imaging and clinical follow-up. The sensitivity, specificity, positive and negative predictive values (PPV and NPV), and accuracy of the two PET imaging in detecting anastomotic recurrence were compared based on the analysis of paired FAPI-FDG PET imaging. Relationships between tracer uptake at surgical wounds and postoperative time were also analyzed. Results: Sensitivity, specificity, PPV, NPV, and accuracy of detecting anastomotic recurrence were 100.0%, 87.3%, 41.7%, 100.0%, and 88.3% for 68Ga-FAPI-04 PET imaging, and 60.0%, 81.8%, 23.1%, 95.7%, and 80.0% for 18F-FDG PET imaging respectively. Compared with non-recurrent patients, the recurrent patients exhibited a significantly higher anastomotic SUVmax and ratio on FAPI-PET imaging (SUVmax : 9.92±4.36 vs. 2.81±1.86, P =0.002; Ratio: 5.11±1.99 vs. 2.23±1.17, P <0.001). 68Ga-FAPI-04 PET displayed a significantly higher SUVmax ratio at surgical wounds than 18F-FDG PET imaging (anastomotic sites: 2.57±1.61 vs. 1.76±0.74, P =0.001; abdominal incision sites: 2.14±1.47 vs. 1.65±1.12, P =0.029). Although 68Ga-FAPI-04 PET signal at surgical wounds showed a slight trend to decrease over time (anastomotic SUVmax : r=-0.2830, P =0.0223; incisional SUVmax : r=-0.4549, P <0.0001), no statistical difference was observed over months post-surgery ( P >0.05). Conclusion: The surveillance power of 68Ga-FAPI-04 PET is superior to 18F-FDG PET in postoperative anastomotic recurrence of gastrointestinal cancer, but the positive predictive value was limited due to wound healing inference. Therefore, combined surveillance methods were suggested instead of relying on 68Ga-FAPI-04 or 18F-FDG PET only.