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

Participants with lung adenocarcinoma underwent contemporaneous 18F-FDG and 68Ga-FAPI PET/CT for an initial assessment. 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-FAPI PET/CT were calculated and compared to evaluate the diagnostic efficacy. In addition, the investigators further investigate the performance of 68Ga-FAPI PET/CT for differentiating invasive adenocarcinoma from adenocarcinoma in situ (pre-invasive lesion) or minimally invasive adenocarcinoma in participants with solitary ground-glass opacity nodules.

Inclusion Criteria:

• (i) aged ≥ 18 years, with newly detected GGNs ≤ 3 cm on LDCT and suspected to be lung cancer, and with no prior treatment;
• (ii) who accepted undergoing paired 18F-FDG and 68Ga-FAPI-46 PET/CT, with completion within one week of each other;
• (iii) with planned surgical resection within one month after PET/CT examinations;
• (iv) with an ability to provide informed consent according to the guidelines of the Clinical Research Ethics Committee.

Exclusion Criteria:

• (i) without surgical treatment;
• (ii) receiving antitumor treatment prior to surgery;
• (iii) whose postoperative pathology revealed adenocarcinoma beyond stage IA or benign pulmonary lesions;
• (iv) with concurrent diagnosis of other malignant tumors;
• (v) with poor image quality or lesions difficult to measure.