Abstract Background Recent studies have demonstrated the utility of fibroblast activation protein inhibitor (FAPI)-positron emission tomography (PET) for cancer diagnosis. We investigated the diagnostic capability of 18 FFAPI-74 PET in patients with lung cancer eligible for surgery. Methods This study included 30 patients (June 2022 to February 2024) who underwent 18 FFAPI-74 PET followed by lung resection at our institution and were pathologically diagnosed with primary lung cancer. The histological types included 24 adenocarcinomas, four squamous cell carcinomas, and two small cell carcinomas or combined small cell carcinomas and adenocarcinomas. Fibroblast activation protein (FAP) expression was evaluated in surgically resected specimens of primary tumors and lymph nodes using immunohistochemical staining. Results All 30 primary lung lesions showed uptake on 18 FFAPI-74 PET (median maximum standardized uptake value SUVmax = 4.8; range: 1.2–15.5). A positive correlation was observed between the SUVmax of 18 FFAPI-74 PET and FAP expression by immunohistochemical staining (FAP-positive area, p = 0.0083; H-score, p = 0.0076). The sensitivity and specificity of 18 FFAPI-74 PET for the diagnosis of lymph node metastases were 75.0% and 88.5%, respectively. In all six cases of significant 18 FFAPI-74 uptake in lymph nodes, FAP expression was confirmed in the lymph node tissue by immunohistochemical staining. Three patients demonstrated lymph node uptake on 18 FFAPI-74 PET due to preoperative chemoradiation therapy or reactive lymph node enlargement/uptake without any malignant findings. Conclusions In resectable early-stage lung cancer, 18 FFAPI-74 PET correlated with histological FAP expression and proved useful for detecting lymph node metastases, although caution is warranted when interpreting the findings after preoperative therapy.
Hiroshima et al. (Tue,) studied this question.