Detection of small renal masses (i.e., ≤4 cm) is increasing, partly due to widespread use of abdominal computed tomography (CT) and magnetic resonance imaging (MRI) and an aging population. Current imaging technologies cannot distinguish between benign and malignant lesions.

Investigators conducted a multicenter phase 3 trial of positron-emission tomography (PET)–CT imaging using [89Zr]Zr-girentuximab, a chimeric monoclonal antibody directed against an antigen associated with renal cell carcinoma, to determine its sensitivity and specificity in detecting clear-cell renal cell carcinoma.

Histopathological confirmation by pathologists blinded to patient information served as the gold standard. A single dose of [89Zr]Zr-girentuximab followed by PET-CT was administered to 332 patients with evidence of a solitary, localised indeterminate renal mass ≤7 cm suspicious for renal cell carcinoma who were scheduled for nephrectomy.

Among the key findings:

• Patients' mean age was 61, 71% were male, and images were evaluable in 96%.

• Mean sensitivity of [89Zr]Zr-girentuximab PET-CT imaging was 85.5%; specificity was 87.0%.

• Mean positive and negative predictive values in all patients were 92.9% and 75.2%, respectively.

• Mean positive and negative predictive values in patients with renal mass ≤4 cm were 93.2% and 78%, respectively.

• All PET-positive lesions were malignant.

• No safety issues were associated with the imaging agent.

This well-done study provides evidence that [89Zr]Zr-girentuximab PET-CT imaging is an important development in the management of small renal masses. Urologists who typically manage patients with this entity have historically used lesion size, characteristics, and rate of change on CT/MRI to make therapy recommendations, with tissue confirmation required in the setting of local ablative interventions.