18F-FDG Versus 68Ga-FAPI-46 as PET Tracer in ER-positive Breast Cancer.

18F-FDG Versus 68Ga-FAPI-46 as PET Tracer in ER-positive Breast Cancer - a Pilot Study.

The extent of breast cancer is an important prognostic factor in patients diagnosed with this disease. Therefore, adequate staging at diagnosis is a requisite for optimal treatment. In all patients diagnosed with locally advanced breast cancer (LABC), distant staging using 18F-FDG PET/CT is recommended. However, the degree of metabolic uptake in the primary breast tumor is significantly lower in the ER+ subtype compared to HER2+ and triple negative breast cancer (TNBC). As a consequence, a suboptimal 18F-FDG uptake in ER+ breast cancer patients can potentially lead to missed distant metastases. Fibroblast-activating protein inhibitor (FAPI) is a recently developed radiotracer that binds to FAP, a stromal antigen overexpressed in more than 90% of epithelial-derived tumors and their metastases. Previous studies all show 68Ga-FAPI PET/CT to have a higher detection rate compared to 18F-FDG PET/CT. However, all previous studies were performed without considering breast cancer subtype. If the metabolic uptake by 68Ga-FAPI-46 is higher in ER+ breast cancer patients, more lesions will be detected, resulting in a more appropriate treatment for these patients. Therefore, in this pilot study, the investigators aim to compare the diagnostic performance of 18F-FDG with 68Ga-FAPI-46 as PET-tracer in ER+ breast cancer patients.

Inclusion Criteria:

• Female patient with histopathologically proven ER+ breast cancer.
• Diagnosed with locally advanced (primary tumor >5 cm and/or presence of axillary lymph node metastases) or recurrent breast cancer, or metastatic breast cancer for which 18F-FDG PET/CT or 18F-FDG PET/MRI staging is performed.
• Willing and able to undergo the study procedures.
• Has personally provided written informed consent.

Exclusion Criteria:

• Age <18
• Pregnancy
• Patients with secondary malignancies (except non-melanoma skin cancer)
• No 18F-FDG PET/CT or 18F-FDG PET/MRI scan.
• Contra-indications for PET/MRI such as pacemaker, aneurysm clips, metallic device in their body, severe claustrophobia, and severe obesity
• Chronic inflammatory disease such as rheumatoid arthritis.
• Patients with severe hepatic or renal impairment (eGFR ≤45mL/min/1.73m²)
• Inability to provide informed consent.