⁶⁸Ga-FAPI-04 PET/CT, a new step in breast cancer imaging: a comparative pilot study with the ¹⁸F-FDG PET/CT

Aim: We aimed to compare the roles of ⁶⁸Ga-FAPI-04 PET/CT and ¹⁸F-FDG PET/CT in the evaluation of primary tumor and metastases in primary and recurrent breast cancer. Materials and method: Twenty female patients with histopathologically confirmed primary and recurrent breast cancer were included in the prospective study. All patients underwent FDG and FAPI PET/CT imaging in the same week. The number of primary and metastatic lesions, SUV_max values, and tumor-to-background ratios (TBR) were recorded from both scans. Data obtained were statistically compared. Results: FAPI PET/CT was superior to FDG in detecting breast lesions, as well as hepatic, bone, lymph node, and cerebral metastases in terms of patient- and lesion-based assessments. The sensitivity and specificity of FAPI in detecting primary breast lesions were 100% and 95.6%, respectively, while the sensitivity and specificity of FDG were 78.2% and 100%, respectively. The SUV_max values of primary breast tumors, lymph nodes, lung metastases, and bone metastases were significantly higher on FAPI imaging than FDG imaging (p < 0.05). However, SUV_max values of hepatic metastases did not exhibit a statistically significant difference between two imaging techniques (p > 0.05). Also, FAPI imaging yielded significantly higher TBR in breast lesions as well as hepatic, bone, brain and lung metastases compared to FDG (p < 0.05). Conclusion: ⁶⁸ Ga-FAPI-04 PET/CT is superior to ¹⁸F-FDG PET/CT in detecting the primary tumor in patients with breast cancer with its high sensitivity, high SUV_max, and high TBR. ⁶⁸ Ga-FAPI-04 PET/CT is also superior to ¹⁸F-FDG PET/CT in detecting lymph node, hepatic, bone, and cerebral metastases because it has lower background activity and higher uptake in subcentimetric lesions.