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

Abstract

In this prospective study, PET findings of 18F-FDG PET/CT in breast cancer staging were compared with 68Ga-FAP inhibitor (FAPI) 04 PET/CT findings in selected cases with relatively low 18F-FDG uptake in the primary tumor or with suspected nodal or distant metastases. Twenty-four women with a median age of 45 years (range, 36-67 years) who underwent initial staging 18F-FDG PET/CT for breast cancer underwent 68Ga-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. The histological subtypes of primary tumors were 11 invasive lobular, 8 invasive ductal, and 5 mucinous subtypes. More intense 68Ga-FAPI-04 uptake (mean, 17.1 ± 7.9; 7.4-38.5) was detected in all primary tumoral lesions compared with 18F-FDG (mean, 6.3 ± 3.9; 1.5-20.5) (P = <0.001, Z = 4.107). Additional lesions showing 68Ga-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 68Ga-FAPI-04 uptake. In 68Ga-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 68Ga-FAPI-04 PET/CT. In a patient with lung and bone metastases, 68Ga-FAPI-04 uptake was higher, and the lung nodule showed only 68Ga-FAPI-04 uptake. In selected low-FDG-affinity breast cancer patients, 68Ga-FAPI-04 PET/CT showed the primary tumor with higher sensitivity and higher SUVmax values compared with 18F-FDG PET/CT. In addition, it is believed that this method may contribute to the management of patients' treatment by increasing the nodal stage.