Diagnostic Accuracy of ⁶⁸Ga-FAPI Versus ¹⁸F-FDG PET in Patients with Various Malignancies

To assess the diagnostic accuracy of ⁶⁸Ga-labeled fibroblast activation protein inhibitor (FAPI) and ¹⁸F-labeled FDG PET for the detection of various tumors, we performed a head-to-head comparison of both imaging modalities across a range of tumor entities as part of our ongoing ⁶⁸Ga-FAPI PET observational trial. Methods: The study included 115 patients with 8 tumor entities who received imaging with ⁶⁸Ga-FAPI for tumor staging or restaging between October 2018 and March 2022. Of those, 103 patients received concomitant imaging with ⁶⁸Ga-FAPI and ¹⁸F-FDG PET and had adequate lesion validation for accuracy analysis. Each scan was evaluated for the detection of primary tumor, lymph nodes, and visceral and bone metastases. True or false positivity and negativity to detected lesions was assigned on the basis of histopathology from biopsies or surgical excision, as well as imaging validation. Results: ⁶⁸Ga-FAPI PET revealed higher accuracy than ¹⁸F-FDG PET in the detection of colorectal cancer (n = 14; per-patient, 85.7% vs. 78.6%; per-region, 95.6% vs. 91.1%) and prostate cancer (n = 22; per-patient, 100% vs. 90.9%; per-region, 96.4% vs. 92.7%). ⁶⁸Ga-FAPI PET and ¹⁸F-FDG PET had comparable per-patient accuracy in detecting breast cancer (n = 16, 100% for both) and head and neck cancers (n = 10, 90% for both modalities). ⁶⁸Ga-FAPI PET had lower per-patient accuracy than ¹⁸F-FDG PET in cancers of the bladder (n = 12, 75% vs. 100%) and kidney (n = 10, 80% vs. 90%), as well as lymphoma (n = 9, 88.9% vs. 100%) and myeloma (n = 10, 80% vs. 90%). Conclusion: ⁶⁸Ga-FAPI PET demonstrated higher diagnostic accuracy than ¹⁸F-FDG PET in the diagnosis of colorectal cancer and prostate cancer, as well as comparable diagnostic performance for cancers of the breast and head and neck. Accuracy and impact on management will be further assessed in an ongoing prospective interventional trial (NCT05160051).