Cancers of the pancreas, bile ducts, stomach and ovaries are dismal diseases with most patients being diagnosed in advanced stages leading to a bad prognosis. These cancers can be difficult to diagnose and sometimes impossible to differentiate from underlying benign conditions. Establishing the correct diagnosis of primary cancer lesions and possible spread to other organs in time is pivotal for choosing the right therapy. Routinely applied staging procedures are however not always reliable. The main aim in this study is to evaluate the diagnostic accuracy of PET/CT with a novel radiotracer, FAPI, in the primary diagnosis of cancers in the pancreas, stomach and bile ducts as well as in patients with primary and recurrent epithelial ovarian cancer (EOC).