Fibroblast activation protein inhibitor-PET/CT in lung cancer: a prospective single-center study with histopathological correlation of fibroblast activation protein expression.

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 [18F]FAPI-74 PET in patients with lung cancer eligible for surgery.

METHODS

This study included 30 patients (June 2022 to February 2024) who underwent [18F]FAPI-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 [18F]FAPI-74 PET (median maximum standardized uptake value [SUVmax] = 4.8; range: 1.2-15.5). A positive correlation was observed between the SUVmax of [18F]FAPI-74 PET and FAP expression by immunohistochemical staining (FAP-positive area, p = 0.0083; H-score, p = 0.0076). The sensitivity and specificity of [18F]FAPI-74 PET for the diagnosis of lymph node metastases were 75.0% and 88.5%, respectively. In all six cases of significant [18F]FAPI-74 uptake in lymph nodes, FAP expression was confirmed in the lymph node tissue by immunohistochemical staining. Three patients demonstrated lymph node uptake on [18F]FAPI-74 PET due to preoperative chemoradiation therapy or reactive lymph node enlargement/uptake without any malignant findings.

CONCLUSIONS

In resectable early-stage lung cancer, [18F]FAPI-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.