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. 68Ga-FAPI has been developed as a tumor-targeting agent. This prospective study is going to investigate the performance and value of 68Ga-FAPI 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. Gallium-68 (68Ga)-conjugated FAP inhibitor (FAPI), a new radiotracer targeting FAP, has been developed for targeting FAP and tumor-stromal visualization. With its fast renal clearance and high tumor-to-background ratio, 68Ga-FAPI has been successfully validated in multi-types of tumors. This study aims to evaluate the performance and value of 68Ga- FAPI 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.