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

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. 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, SUVmax values, and tumor-to-background ratios (TBR) were recorded from both scans. Data obtained were statistically compared. 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 SUVmax values of primary breast tumors, lymph nodes, lung metastases, and bone metastases were significantly higher on FAPI imaging than FDG imaging (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). 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 SUVmax, 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.