Gallium-68-Labelled Fibroblast Activation Protein Inhibitor PET/CT in the clinical diagnosis and management of breast cancer: Comparison with [18F]FDG PET/CT

Abstract

Purpose To evaluate the diagnostic accuracy and clinical impact of gallium-68-labelled fibroblast activation protein inhibitor ([68Ga]Ga-FAPI) PET/CT in primary and metastatic breast cancer and compare the results with those of standard-of-care imaging (SCI) and [18F]Fluorodeoxyglucose (FDG) PET/CT. Methods Patients with diagnosed or suspected breast cancer who underwent concomitant [68Ga] Ga-FAPI (FAPI-46) and [18F]FDG PET/CT scans from October 2019 to March 2022 were retrospectively analysed. Breast ultrasound (US) imaging was performed in all treatment-naïve patients as SCI. The maximum standard uptake value (SUVmax), tumour-to-background ratio (TBR), lesion detection rate, and tumour-node-metastasis (TNM) classifications between [68Ga]Ga-FAPI and [18F]FDG PET/CT were evaluated, and compared. Results Twenty-eight women (median age, 52.5 y; range, 28–80 y) were included. Among them, 5 patients underwent evaluation for a definitive diagnosis of suspected breast lesions, 9 underwent initial staging, and 14 were evaluated for the detection of recurrence. The sensitivities of breast US, [18F]FDG, and [68Ga]Ga-FAPI PET/CT for detecting primary breast tumours were 80%, 70%, and 100%, respectively. Regarding the diagnosis of recurrent/metastatic lesions, the per-lesion detection rate of [68Ga]Ga- FAPI PET/CT was significantly higher than that of [18F]FDG, which including local and regional recurrence (128 vs. 88), neck lymph node (LN) metastases (33 vs. 15), abdomen LN metastases (28 vs. 3), bone metastases (146 vs. 59), and liver metastases (28 vs. 11). Compared with [18F]FDG, [68Ga]Ga-FAPI PET/CT upstaged five patients’ TNM staging/re-staging (7/27, 26%) and changed five patients’ clinical management (5/27, 19%). Compared to SCI, [68Ga]Ga-FAPI upstaged ten patients' TNM staging/re-staging (9/27, 33%) and changed the therapeutic regimen of seven patients (7/27, 26%). There was no significant association between FAPI-derived SUVmax and receptor status/histologic type in both primary and metastatic lesions. Conclusion [68Ga]Ga-FAPI PET/CT was superior to [18F]FDG in diagnosing primary and metastatic breast cancer, with higher radiotracer uptake and TBR, especially in the detection of primary/recurrent tumour, abdominal LN metastases, liver, and bone metastases. [68Ga]Ga-FAPI PET/CT is superior to [18F]FDG and SCI in TNM staging and may improve tumour staging, recurrence detection, and implementation of necessary treatment modifications.