An experimental gallium-68 (Ga-68)-labeled PET radiotracer detected 97.9% of lesions in patients with clear cell renal cell carcinoma, according to research presented October 20 at the European Association of Nuclear Medicine (EANM) meeting in Vienna.
The tracer targets carbonic anhydrase IX (CAIX), a protein highly expressed in clear cell renal cell carcinoma (ccRCC), and could potentially give clinicians a more complete picture of the location and extent of a patient’s disease, according to the study authors.
“CAIX gives us a highly selective biological target,” said lead author Esra Arslan, MD, of the University of Health Sciences in Istanbul, Turkey, in a EANM news release. “It is expressed at a very high rate in ccRCC, while expression in normal renal tissue remains minimal. This gives us the potential to distinguish tumor from surrounding healthy tissue much more clearly.”
While F-18 FDG is the most commonly used PET radiotracer in cancer, it measures non-cancer specific glucose metabolism by tumors, and researchers are developing more targeted imaging approaches. The CAIX-targeting agent Ga-68 DPI-4452 has shown promise in early research in ccRCC, and in this study, the group tested it in a larger prospective trial.
The group enrolled 68 patients with RCC and compared Ga-68 DPI-4452 PET/CT scans with F-18 FDG PET/CT scans among the participants. Across 492 true lesions evaluated in the study, Ga-68 DPI-4452 PET/CT detected 90.9%, compared with 56.7% using F-18 FDG PET/CT. The difference was even greater in ccRCC, where Ga-68 DPI-4452 PET/CT detected 97.9% of lesions compared with 47.1% using ¹⁸F-FDG PET/CT.
The difference was particularly striking in brain metastases, the researchers reported. Ga-68 DPI-4452 PET/CT detected all identified brain metastases, with a median maximum tumor-to-background ratio of 281.3 compared with 0.7 for F-18 FDG. Ga-68 DPI-4452 PET/CT also detected all identified lung metastases compared with around half using F-18 FDG PET/CT, while lymph-node detection was 95.0% versus 68.9%.
The researchers suggested potential roles for CAIX-targeted PET/CT may be in initial staging before nephrectomy or metastasectomy, restaging when recurrence is suspecte, or as part of a theranostic approach in which Ga-68 DPI-4452 PET/CT could help identify patients suitable for treatment with lutetium-177 DPI-4452.
“Ga-68 DPI-4452 has the potential to become a valuable tool across several stages of RCC management. However, it is premature to claim that this agent represents a ‘new molecular imaging standard’ without validation in larger, multicentre studies stratified by subtype,” Arslan said.
