Fibroblast activation protein (FAP) is overexpressed in cancer-associated fibroblasts (CAFs), which constitute a major proportion of cells within the tumor microenvironment, especially in breast cancer. Previous studies have demonstrated that FAPI PET/CT performs well in cases of epithelial tumors, including breast cancer. This prospective study is going to investigate the performance and value of Al18F-NOTA-FAPI-04 PET/CT in patients with breast cancer.

Breast cancer is a complex, heterogeneous disease comprising numerous distinct biological subtypes characterized by variant pathobiological features and clinical behaviors. 18F-fluorodeoxyglucose (18F-FDG) PET/CT, an essential imaging modality in the characterization of metabolism within the tumor, has successfully evolved in the diagnosis, staging, and assessment of treatment response in patients with breast cancer. Cancer-associated fibroblasts (CAFs) are a crucial component of the tumor stroma with diverse functions. Fibroblast activation protein (FAP), a type II membrane-bound glycoprotein from the dipeptidyl peptidase-4 family, is highly expressed in the CAFs of several epithelial carcinomas, including breast cancer, coupled with relatively low expression in normal tissue. Based on this characteristic, many small-molecule inhibitors of FAP (FAPIs) labeled with radioactive tracers (68Ga, 18F, or 177Lu) have been synthesized as theranostic radiotracers for cancer. Previous studies on FAPI PET/CT tumor imaging have focused on the 68Ga radionuclide rather than 18F. As 18F-labeled FAPI has more favorable physical properties, high production capacity, and good imaging characteristics, it may be an ideal agent for PET imaging. Therefore, this study aims to evaluate the performance and value of Al18F-NOTA-FAPI-04 PET/CT in patients with breast cancer.

Inclusion Criteria:

• age 18-80 years old;
• newly diagnosed BC confirmed by biopsy or with BI-RADS category 4C or 5 lesions by US or MG;
• BC clinical stagecT1-3 cN0-3 M0;
• no prior treatment for BC.

Exclusion Criteria:

• pregnancy;
• breastfeeding;
• patients who were unwilling to undergo PET/CT scans.