To evaluate the potential usefulness of 68Ga-DOTA-FAPI-04 positron emission tomography/computed tomography (PET/CT) for the diagnosis of primary and metastatic lesions in various types of cancer, compared with 18F-FDG PET/CT.

Subjects with various types of cancer underwent contemporaneous 68Ga-DOTA-FAPI-04 and 18F-FDG PET/CT either for an initial assessment or for recurrence detection. Tumor uptake was quantified by the maximum standard uptake value (SUVmax). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of 18F-FDG and 68Ga-DOTA-FAPI-04 PET/CT were calculated and compared to evaluate the diagnostic efficacy.

Inclusion Criteria:

• (i) adult patients (aged 18 years or order); (ii) patients with suspected or newly diagnosed or previously treated malignant tumors (supporting evidence may include magnetic resonance imaging (MRI), CT, tumor markers and pathology report); (iii) patients who had scheduled both 18F-FDG and 68Ga-DOTA-FAPI-04 PET/CT scans; (iv) patients who were able to provide informed consent (signed by participant, parent or legal representative) and assent according to the guidelines of the Clinical Research Ethics Committee.

Exclusion Criteria:

• (i) patients with non-malignant lesions; (ii) patients with pregnancy; (iii) the inability or unwillingness of the research participant, parent or legal representative to provide written informed consent.