Superiority of [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT to [¹⁸F]FDG PET/CT in the evaluation of thymic epithelial tumours.

Abstract

The purpose of this study is to compare the ability of [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT and [¹⁸F]FDG PET/CT to stratify the malignancy and invasiveness of thymic epithelial tumours (TETs). From April 2021 to November 2022, participants with suspected TETs confirmed by histopathology or follow-up imaging were prospectively analysed. All participants underwent [¹⁸F]FDG and [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT within 1 week. Clinical characteristics, CT features, and metabolic parameters (maximum standardized uptake value [SUV_max] and tumour-to-mediastinum ratio [TMR]) of subjects with different pathological types and stages were compared. The diagnostic capacities of [¹⁸F]FDG and [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT were compared using receiver operating characteristic (ROC) curves and McNemar's test. Fifty-seven participants were included. [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT was superior to [¹⁸F]FDG PET/CT in differentiating thymomas from thymic carcinomas (TCs) (AUC: 0.99 vs. 0.90, P = 0.02). Logistic regression revealed that SUV_max-FAPI (P = 0.04) was a significant predictive factor for TCs. SUV_max-FAPI and TMR_-FAPI showed an excellent ability to differentiate low-risk thymomas (types A, AB, and B1), high-risk thymomas (types B2 and B3), and TCs (both P < 0.001). In thymomas, only SUV_max-FAPI (P < 0.001), TMR_-FAPI (P < 0.001), and nonsmooth edges (P = 0.02) were significantly higher in the advanced-stage (Masaoka-Koga [MK] stage III/IV) group than in the early-stage group (MK stage I/II). Compared with [¹⁸F]FDG PET/CT, [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT showed significantly higher specificity (67% [46 of 69] vs. 93% [64 of 69], P < 0.001) in the detection of lymph node metastases and higher sensitivity (49% [19 of 39] vs. 97% [38 of 39], P < 0.001) in evaluating distant metastases. Both SUV_max-FAPI and TMR_-FAPI were correlated with FAP expression (both r = 0.843, P < 0.001). [⁶⁸Ga]Ga-DOTA-FAPI-04 PET/CT was superior to [¹⁸F]FDG PET/CT in evaluating the World Health Organization (WHO) classification, MK staging, and metastatic status of TETs. ChiCTR2000038080, registration date 2020-09-09, https://www.chictr.org.cn/com/25/showproj.aspx?proj=61192.