The Role of⁶⁸Ga-FAPI PET/CT for Patients with Malignancies of the Lower Gastrointestinal Tract: First Clinical Experience

Abstract

For oncologic management or radiotherapy planning, reliable staging tools are essential. The recent development of quinoline-based ligands targeting cancer-associated fibroblasts demonstrated promising preclinical and clinical results. The current study aimed to evaluate the role of fibroblast activation protein inhibitor (FAPI) PET/CT as a first clinical analysis for primary malignancies within the lower gastrointestinal tract (LGT). <b>Methods:</b>⁶⁸Ga-FAPI PET/CT was performed on a cohort of 22 patients with LGT tumors, including 15 patients with metastatic disease, 1 patient with suspected local relapse, and 6 treatment-naïve patients. Uptake of ⁶⁸Ga-FAPI-04 and ⁶⁸Ga-FAPI-46 was quantified by SUV_max and SUV_mean After comparison with standard imaging, changes in tumor stage or localization and in oncologic or radiooncologic management were recorded. <b>Results:</b> The highest uptake of FAPI tracer was observed in liver metastases and anal cancer, with an SUV_max of 9.1 and 13.9, respectively. Because of low background activity in normal tissue, there was a high tumor-to-background ratio of more than 3 in most lesions. In treatment-naïve patients, TNM was changed in 50%, whereas in patients with metastases, new findings occurred in 47%. In total, FAPI imaging caused a high, medium, and low change in oncologic or radiooncologic management in 19%, 33%, and 29%, respectively. For almost every patient undergoing irradiation, target volume delineation was improved by ⁶⁸Ga-FAPI PET/CT. <b>Conclusion:</b> The present study demonstrated that both primary and metastatic LGT tumors were reliably detected by ⁶⁸Ga-FAPI PET/CT, leading to relevant changes in TNM status and oncologic or radiooncologic management. ⁶⁸Ga-FAPI PET/CT seems to be a highly promising imaging agent for the diagnosis and management of LGT tumors, potentially opening new applications for tumor staging or restaging.