A pilot study of [⁶⁸Ga]Ga-fibroblast activation protein inhibitor-04 PET/CT in renal cell carcinoma

Objectives As a promising positron emission tomography (PET) tracer, [Ga-68]Ga-fibroblast activation protein inhibitor-04([Ga-68]Ga-FAPI-04) performs better than 2-[F-18]fluoro-2-deoxy-D-glucose ([F-18]FDG) at diagnosing primary and metastatic lesions in patients with various types of cancer. We investigated the utility of [Ga-68]Ga-FAPI-04 PET/CT for the detection of primary and metastatic lesions in renal cell carcinoma (RCC). [F-18]FDG PET/CT were used for comparison. Methods Twenty-two patients with suspected RCC or recurrent RCC were enrolled in our study. Among these patients, 14 were newly diagnosed with RCC, 3 had recurrent RCC, and 5 were excluded from further analysis due to having benign renal tumours. Seventeen patients with RCC underwent [Ga-68]Ga-FAPI-04 PET/CT, and 6 of them also received [F-18]FDG PET/CT. The positive detection rates were calculated and compared with those in patients who underwent both scans. Results Data from 17 patients with RCC (median age: 60.5 years, interquartile range [IQR]: 54-70 years) were evaluated. The positive detection rate of [Ga-68]Ga-FAPI-04 PET/CT for RCC was 64.7% (11/17). Lymph node metastases (n = 44), lung metastasis (n = 1), and bone metastasis (n = 1) were detected. Six patients with RCC underwent [Ga-68]Ga-FAPI-04 and [F-18]FDG PET/CT. [Ga-68]Ga-FAPI-04 PET/CT showed a higher positive detection rate than [F-18]FDG PET/CT in detecting RCC (83.3% [5/6] vs. 50% [3/6], P = 0.545). Additionally, [Ga-68]Ga-FAPI-04 PET/CT has higher SUVmax (3.20 [IQR: 2.91-5.80 vs. 2.71 [IQR: 2.13-3.10], P = 0.116) and tumour-to-background ratio (TBR) values (1.60 [IQR: 1.33-3.67] vs. 0.86 [0.48-1.21], P = 0.028) than [F-18]FDG PET/CT. Conclusions These findings suggest that [Ga-68]Ga-FAPI-04 PET/CT has potential value in RCC diagnosis. Further studies are warranted to validate these results.