Cancers of unknown primary (CUP) account for 3-5% of all malignancies. The prognosis of patients diagnosed with CUP is poor, with a median overall survival of 9-12 months. Despite improvements in conventional diagnostic processes, the tissue of origin (ToO) is identified in <30% of CUP patients. PET/CT is increasingly used to determine the ToO, with the most commonly used PET radiotracer being the glucose analogue fluorine-18 fluorodeoxyglucose (FDG). Although PET/CT can change CUP patient management and identify primary sites, FDG has limited sensitivity for detecting some cancers, such as CUP. It has been reported that fibroblast activation protein (FAP) is highly expressed in some tumours, including CUP. 68Ga-FAPI (experimental drug) is a radiotracer that can specifically bind to FAP, and may enable the primary cancer site to be viewed using PET imaging. It is hypothesised that the use of 68Ga-FAPI-PET/CT will increase likely ToO diagnosis from 30% with current standard of care to 60%.
This is a prospective single arm cohort study designed to evaluate the diagnostic ability of 68Ga-FAPI-PET/CT scan in determining likely tissue of origin in Cancer of Unknown Primary (CUP) patients not identified by standard of care. Patients with CUP will be either treatment naïve or starting second-line treatment.