The Diagnostic Accuracy and Clinical Value of FAPI PET in Pleural Mesothelioma

Inclusion Criteria: * Patients with pleural lesions suspicious of pleural mesothelioma and referred to pleural biopsy. * Undergone/undergoing FDG PET/CT as part of the diagnostic workup of a suspicious PM lesion. * Considered physically and mentally able to participate in the research project. * Understands the study subject information and able to consent to project participation. * 18-years or older Exclusion Criteria: * Patients with an imminent need for surgery or in an emergency * Known concurrent other malignancy with active treatment within the last 1 year; non-melanoma skin cancer and cervical cancer in situ are exempt. * Pregnant or breastfeeding women. * Fertile women (women of childbearing potential) who could - theoretically - be pregnant (i.e., unknown pregnancy status). Fertile women will be tested for pregnancy (by urine humane choriogonadotropin (HCG) or serum HCG) within 48h before FAPI PET/CTs, both at primary staging and restaging. Study subjects can participate in the study if the pregnancy test is negative (i.e., not pregnant). * Subjects unable to undergo PET/CT: e.g., weighing more than 180 kg (weight limit scanner), unable to fit within the imaging gantry, inability to remain still for the duration of the examination, or with known severe claustrophobia unresponsive to oral anxiolytics or severe fear of needles. * Subjects with any medical condition or other circumstances that, in the opinion of the Investigator, would significantly decrease the reliability of data, achievement of study objectives or completing the study. * History of allergic reactions / hypersensitivity attributed to \[18F\]FDG or FAPI-tracers.