[¹⁸F]RCCB6 immunoPET/CT detects primary clear cell renal cell carcinoma

A 51-year-old female presented with hematuria and lumbar pain, persisting for one month. Initial computed tomography (CT) revealed a suspicious mass in the upper pole of the right kidney. Positron emission tomography/CT (PET/CT) scanning was recommended to characterise the mass and exclude potential distant metastases. ¹⁸F-fluorodeoxyglucose ([¹⁸F]FDG) PET/CT with an injection dose of 6.69 mCi demonstrated a 36 × 29 mm heterogeneous mass with ill-defined borders in the ventral aspect of the middle-upper pole of the enlarged right kidney. Considering the comparable ¹⁸F-FDG uptake of the mass (SUVmax = 2.53) with that of renal parenchyma (SUVmax = 5.10 − 6.32) at delayed imaging, CD70-targeted immunoPET/CT was further recommended for differential diagnosis and comprehensive characterisation [1‐3]. [¹⁸F]RCCB6 immunoPET/CT (injection dose: 2.11 mCi) at two hours post-injection (p.i.) demonstrated an intense uptake of the mass (SUVmax = 156, red arrowhead) with high bilateral renal cortical uptake (SUVmax = 116, yellow arrowhead). However, delayed imaging at five hours p.i. delineated the mass (SUVmax = 129, blue arrowhead) with significantly decreased renal cortical background (SUVmax = 56). Histopathological examination of the resected specimen revealed the cells arranged in nests with abundant clear cytoplasm and characteristic thin-walled vascular networks. The tumour was classified as Fuhrman grade II, stage pT1bN0M0 clear cell renal cell carcinoma (ccRCC). Immunohistochemistry demonstrated strong membranous CD70 expression and positive carbonic anhydrase IX (CA-IX) staining in tumour cells with negative staining in non-neoplastic tissue. Although [¹⁸F]RCCB6 detects metastatic ccRCC, the case highlights the potential value of [¹⁸F]RCCB6 in detecting ¹⁸F-FDG-negative primary ccRCC at delayed imaging. Further research is warranted to establish the imaging protocols and optimise the tracers’ pharmacokinetics. …