[18F]F-FAPI PET-CT to Identify Carcinoma of Unknown Primary Origin

Carcinoma of unknown primary origin (CUP) is a diverse group of cancers defined by the presence of metastatic disease with no identified primary tumor after exhaustive diagnostic work-up. Absence of a known targetable primary tumor precludes patients from receiving tumor-specific evidence-based therapies which significantly impacts the life expectancy of CUP patients. In this investigator-initiated and patient association-driven, multi-center, prospective clinical study we aim to detect the primary tumor by PET-CT using the novel radiotracer [18F]F-fluoro fibroblast activation protein inhibitor (F-FAPI). We will include 50 patients (aged >18 year) who have been diagnosed with CUP after standard diagnostic work-up including FDG PET-CT. Participation in the study entails a one-time [18F]F-FAPI PET-CT examination in one of the six study centers (UMC Groningen, UMC Utrecht, Antoni van Leeuwenhoek, Radboudumc, Maastricht UMC, Erasmus MC). For the interpretation of images, central reading will be performed and results will be made available to the treating physician with an accompanying recommendation for additional diagnostics and/or treatment. After 6 months, the results of the [18F]F-FAPI PET-CT will be compared with patient follow up, including clinical, radiological and pathological outcome parameters. These findings will holistically be discussed in a multidisciplinary Truth Panel meeting to determine a uniform verdict with regard to the clinical value of [18F]F-FAPI for CUP. We hypothesize that [18F]F-FAPI PET-CT will detect the primary tumor in at least 15% of our CUP patients.¬