[Evaluation of 18F-fibroblast activation protein inhibitor-42 PET/CT in lymphangioleiomyomatosis and its correlation with vascular endothelial growth factor-D].

Objective: To evaluate the potential value of ¹⁸F-fibroblast activation protein inhibitor (FAPI)-42 PET/CT in the detection of pulmonary lymphangioleiomyomatosis (LAM) lesions, and its correlation with vascular endothelial growth factor-D (VEGF-D). Methods: This retrospective study enrolled 39 female LAM patients (median age 36 years, IQR 29-42) from the Department of Respiratory and Critical Care Medicine, The First Affiliated Hospital of Guangzhou Medical University (May 2021-April 2024), along with 39 contemporaneously recruited age-matched female controls diagnosed with pulmonary arterial hypertension (median age 35 years, IQR 28-40). The maximum standardized uptake values (SUVmax) of LAM-associated lesions (mediastinal/retroperitoneal/pelvic lymphangioleiomyomas, renal hamartomas) were compared with the blood pool SUVmax in corresponding regions of controls. Lesions in LAM patients who underwent both ¹⁸F-FAPI-42 PET/CT and contrast-enhanced CT within one year were assessed visually. Semi-quantitative PET parameters of lymphangioleiomyomas and renal hamartomas--including SUVmax, target-to-background ratio (TBR), FAPI-avid tumor volume (FTV), and total lesion FAP expression (TLF)--were analyzed for correlation with serum VEGF-D levels. Data analyses were performed using the following statistical methods: Wilcoxon rank-sum test, McNemar's test, Mann-Whitney U test, and Pearson or Spearman correlation analyses. Results: ¹⁸F-FAPI-42 PET/CT detected significantly more lymphangioleiomyomas than contrast-enhanced CT (all P<0.05), although no statistical difference was observed for renal hamartomas (P=0.157). SUVmax of mediastinal/retroperitoneal/pelvic lymphangioleiomyomas and renal hamartomas in LAM patients were significantly higher than those in controls (all P<0.05). VEGF-D levels showed positive correlations with TBR (r=0.390, P=0.033), FTV (r=0.463, P=0.01), and TLF (r=0.490, P=0.006) of lymphangioleiomyomas, as well as FTV (r=0.736, P=0.006) and TLF (r=0.670, P=0.015) of renal hamartomas. Conclusion: ¹⁸F-FAPI-42 PET/CT demonstrates potential application value in assessing lesions in patients with LAM, with some PET semi-quantitative indexes showing a positive correlation with VEGF-D.