Ga-68-FAPI-04 PET/CT in Selected Breast Cancer Patients With Low FDG Affinity A Head-to-Head Comparative Study

PurposeIn this prospective study, PET findings of F-18-FDG PET/CT in breast cancer staging were compared with Ga-68-FAP inhibitor (FAPI) 04 PET/CT findings in selected cases with relatively low F-18-FDG uptake in the primary tumor or with suspected nodal or distant metastases.Patients and MethodsTwenty-four women with a median age of 45 years (range, 36-67 years) who underwent initial staging F-18-FDG PET/CT for breast cancer underwent Ga-68-FAPI-04 PET/CT imaging within the same week. SUVmax and quantities of primary tumors and locoregional and distant metastatic lesions were recorded from both images, and these data were compared statistically.ResultsThe histological subtypes of primary tumors were 11 invasive lobular, 8 invasive ductal, and 5 mucinous subtypes. More intense Ga-68-FAPI-04 uptake (mean, 17.1 & PLUSMN; 7.9; 7.4-38.5) was detected in all primary tumoral lesions compared with F-18-FDG (mean, 6.3 & PLUSMN; 3.9; 1.5-20.5) (P = <0.001, Z = 4.107). Additional lesions showing Ga-68-FAPI-04 uptake in the breast were detected in 29.2% (n = 7) of patients. In 8.3% (n = 2) of the patients, the primary lesion showed only Ga-68-FAPI-04 uptake. In Ga-68-FAPI-04 PET/CT, 25% (n = 6) of the patients showed more lymph node involvement and more intense uptake in the ipsilateral axilla. In addition, infraclavicular (level 3) lymph nodes in 4 patients (16.7%), supraclavicular lymph nodes in 1 patient, and internal mammary lymph nodes in 1 patient were detected only on Ga-68-FAPI-04 PET/CT. In a patient with lung and bone metastases, Ga-68-FAPI-04 uptake was higher, and the lung nodule showed only Ga-68-FAPI-04 uptake.ConclusionsIn selected low-FDG-affinity breast cancer patients, Ga-68-FAPI-04 PET/CT showed the primary tumor with higher sensitivity and higher SUVmax values compared with F-18-FDG PET/CT. In addition, it is believed that this method may contribute to the management of patients' treatment by increasing the nodal stage.