Initial clinical experience using 68 Ga-FAPI-46 PET/CT for detecting various cancer types.

Objective: Numerous studies have shown that gallium-68-labeled fibroblast activation protein inhibitor ( ⁶⁸ Ga-FAPI) positron emission tomography/computed tomography (PET/CT) scans would yield high intra-tumoral tracer uptake and low uptake in normal tissues as background, thus allowing for excellent visualization of lesions in the cancer microenvironment. This study set out to compare the suitability of novel ⁶⁸ Ga-FAPI-46 PET versus routine fluorine-18-fluorodeoxyglucose ( ¹⁸ F-FDG) PET and other few cases of ⁶⁸ Ga-DOTATATE/ ⁶⁸ Ga-Pentixafor PET/CT for the assessment of different types of cancer.
Subjects and Methods: A retrospective analysis of 11 patients (6 males, 5 females; average age: 53 years, range: 10-58 years) with histopathologically confirmed, well-differentiated adenocarcinoma, medullar thyroid cancer (MTC), papillary thyroid carcinoma (PTC), cervical, gastric, glioblastoma multiform (GBM), colon, Ewing's sarcoma, and breast cancer was performed. These patients underwent PET/CT scans using four different radiotracers (9 ¹⁸ F-FDG, 11 ⁶⁸ Ga- FAPI, 3 ⁶⁸ Ga-DOTATATE, and 1 ⁶⁸ Ga-Pentixafor). The patients' PET/CT images were visually evaluated for cancer detection, and analyzed semi-quantitatively through image- derived metrics, such as target-to-background ratio (TBR) and maximum standardized uptake value (SUVmax), for recurrence and metastasis.
Results: The study of 11 patients revealed that ⁶⁸ Ga-FAPI-46 was more effective than other tracers for detecting metastases, with 55 vs. 49 metastases in the lymph nodes, 4 vs. 3 in the liver, and 4 vs. 3 in the bones detected in comparison to ¹⁸ F-FDG. No significant differences were observed in ⁶⁸ Ga-DOTATATE and ⁶⁸ Ga-Pentixafor PET images. In addition, in five patients, the SUVmax and TBR values in ⁶⁸ Ga-FAPI-46 PET images were significantly higher than those in ¹⁸ F-FDG PET images for lymph nodes and bone metastases. Although the SUVmax in ⁶⁸ Ga-FAPI-46 and ¹⁸ F-FDG PET images for liver metastases was comparable, ⁶⁸ Ga-FAPI- 46 had a significantly higher TBR than ¹⁸ F-FDG.
Conclusion: Our findings suggest that FAPI PET/CT is not suitable for evaluating GBM and Ewing sarcoma but generally outperforms ¹⁸ F-FDG PET/CT in various types of breast cancer, gastrointestinal, gynecological, PTC and MTC. However, larger trials are needed to validate these preliminary findings.