Detection and Outcomes in Metastatic Invasive Lobular Breast Cancer Through Novel F-18 FAP PET

This study is a pilot clinical imaging trial of a prospective, head-to-head comparison of 18F-Fibroblast Activation Protein Inhibitor (FAPI)-74 PET/CT versus standard-of-care 18F-Fluorodeoxyglucose (FDG) PET/CT in 15 patients with metastatic invasive lobular breast cancer (ILC). Patients will undergo both 18F-FDG PET/CT and 18F-FAPI-74 PET/CT within a 2-week period (14 days + 7 days) to compare lesions, tumor detection rates, and PET lesion intensity, as well as to assess the clinical value of the PET scans from the treating physician's and the patient's perspective.

Inclusion Criteria: * Provision of signed and dated informed consent form * Stated willingness to comply with all study procedures and lifestyle considerations and availability for the duration of the study * Females; Age \> 18 years of age * Diagnosis of invasive lobular breast cancer, with pathologically confirmed metastatic disease. * ECOG performance status 0-2 * No planned change in anticancer therapy between FDG and FAPI PET scans Exclusion Criteria: * Patients who are pregnant or lactating * Patients who cannot undergo PET/CT scanning * Patients with total serum bilirubin or serum creatinine \> 1.5 times the upper limit of normal