<sup>68</sup>Ga-FAPI-04 PET/CT in Non–Small Cell Lung Cancer: Accurate Evaluation of Lymph Node Metastasis and Correlation with Fibroblast Activation Protein Expression
Chongjiao Li, Qiongrong Chen, Yueli Tian, Jie Chen, Kui Xu, Zhiwei Xiao, Juan Zhong, Jianyuan Wu, Bing Wen, Yong He
Abstract
Fibroblast activation protein (FAP) is a promising diagnostic and therapeutic target in various solid tumors. This study aimed to assess the diagnostic efficiency of <sup>68</sup>Ga-labeled FAP inhibitor (FAPI)–04 PET/CT for detecting lymph node metastasis in non–small cell lung cancer (NSCLC) and to investigate the correlation between tumor <sup>68</sup>Ga-FAPI-04 uptake and FAP expression. <b>Methods:</b> We retrospectively enrolled 136 participants with suspected or biopsy-confirmed NSCLC who underwent <sup>68</sup>Ga-FAPI-04 PET/CT for initial staging. The diagnostic performance of <sup>68</sup>Ga-FAPI-04 for the detection of NSCLC was evaluated. The final histopathology or typical imaging features were used as the reference standard. The SUV<sub>max</sub> and SUV<sub>mean</sub>, <sup>68</sup>Ga-FAPI–avid tumor volume (FTV), and total lesion FAP expression (TLF) were measured and calculated. FAP immunostaining of tissue specimens was performed. The correlation between <sup>68</sup>Ga-FAPI-04 uptake and FAP expression was assessed using the Spearman correlation coefficient. <b>Results:</b> Ninety-one participants (median age, 65 y [interquartile range, 58–70 y]; 69 men) with NSCLC were finally analyzed. In lesion-based analysis, the diagnostic sensitivity and positive predictive value of <sup>68</sup>Ga-FAPI-04 PET/CT for detection of the primary tumor were 96.70% (88/91) and 100% (88/88), respectively. In station-based analysis, the diagnostic sensitivity, specificity, and accuracy for the detection of lymph node metastasis were 72.00% (18/25), 93.10% (108/116), and 89.36% (126/141), respectively. Tumor <sup>68</sup>Ga-FAPI-04 uptake (SUV<sub>max</sub>, SUV<sub>mean</sub>, FTV, and TLF) correlated positively with FAP expression (<i>r</i> = 0.470, 0.477, 0.582, and 0.608, respectively; all <i>P</i> ≤ 0.001). The volume parameters FTV and TLF correlated strongly with FAP expression in 31 surgical specimens (<i>r</i> = 0.700 and 0.770, respectively; both <i>P</i> < 0.001). <b>Conclusion:</b><sup>68</sup>Ga-FAPI-04 PET/CT had excellent diagnostic efficiency for detecting lymph node metastasis, and <sup>68</sup>Ga-FAPI-04 uptake showed a close association with FAP expression in participants with NSCLC.