CD70 and nonpapillary renal cell carcinoma: In a ccRCC patient-derived xenograft model, (18F)RCCB6 exhibited substantial tumor-specific uptake (10.63% ± 1.21% ID/g), with CD70 blockade significantly reducing this signal (0.53% ± 0.04% ID/g; p = 0.002), confirming target engagement.