A Dutch multicenter trial is set to evaluate whether [18F]F-FAPI PET-CT can find primary tumors in adults with cancer of unknown primary after standard imaging fails. The study plans to enroll 50 participants and uses PET-CT targeting FAP to improve diagnostic resolution in a group where clinical staging and treatment selection often depend on identifying the tissue of origin. If the design confirms meaningful detection rates and patient management impact, FAPI PET could shift diagnostic algorithms for CUP and accelerate pathway selection for targeted oncology decisions.