Abstract
P329
Introduction: In recent years, quinoline-based fibroblast activation protein inhibitors (FAPIs) have shown promising results in the diagnosis of cancer. PET imaging using [68Ga]Ga-FAPI shows a greater tumour-to-background ratio (TBR) than [18F]FDG in various types of cancer, particularly in breast cancer. However, the further clinic role of [68Ga]Ga-FAPI PET/CT in the detection, staging/re-staging, and cancer management of breast cancer have not been systematically investigated. In this study, we investigated the diagnostic accuracy and clinical impact of [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]FDG PET/CT.
Methods: This was a single-centre post-hoc retrospective study of a sub-cohort of patients from a previously acquired database. 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),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 patient-based tumour detectability, [68Ga]Ga-FAPI was superior to [18F]FDG PET for primary tumour detection (92% [12/13] vs. 85% [11/13], p=1.000), local recurrence or metastases (100% [21/21] vs. 81% [17/21], p=0.125), neck lymph node (LN) metastases (100% [4/4] vs. 50% [2/4], p=0.500), abdomen LN metastases (100% [4/4] vs. 25% [1/4], p=0.250), bone metastases (100% [12/12] vs. 83% [10/12] , p=0.500) and liver metastases (100% [6/6] vs. 50% [3/6], p=0.250). 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 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.
Conclusions: [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.
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