New PET scan finds 97.9% of clear cell kidney cancer lesions

A new PET approach was tested against the standard scan: in clear cell renal cell carcinoma, the most common form of kidney cancer, it detected 97.9% of lesions, against 47.1% with the standard FDG scan.

Renal cell carcinoma is the most common kidney cancer, and clear cell is its most frequent subtype. The usual PET tracer, ¹⁸F-FDG, measures glucose metabolism. In the kidneys, that signal is hard to read: the organ takes up high levels of glucose naturally and excretes large amounts of tracer through the urine, so tumors can blend into their surroundings. Some low-grade tumors also absorb little FDG, which makes them harder to see.

The team, led by Esra Arslan, chose a different target: carbonic anhydrase IX, or CAIX, a protein that is highly expressed in clear cell tumors while showing "minimal expression in normal renal tissue". In a prospective multicenter study of 68 patients, the CAIX-targeted tracer [⁶⁸Ga]Ga-DPI-4452 detected 90.9% of 492 true lesions, against 56.7% for FDG. Patient-level diagnostic accuracy in clear cell tumors reached 98.2%, against 77.2%. Tumor uptake was about five times higher than with FDG, and the tumor-to-background ratio around ten times greater. "CAIX gives us a highly selective biological target," Arslan said.

The gap was widest in the brain, where the new tracer detected all identified brain metastases, with a median maximum tumor-to-background ratio of 281.3, against 0.7 for FDG. It also caught all identified lung metastases, against around half with FDG, and detected 95.0% of lymph-node lesions, against 68.9%. Liver metastases were the exception across the whole cohort, where FDG did better, reflecting lower and more variable CAIX expression in some non-clear cell subtypes. Within the clear cell group, the new tracer again came out ahead.

For patients, the practical effect is that the scan changed the plan itself. The new tracer altered clinical management or disease stage in 30.9% of patients, against 5.9% with FDG, uncovering recurrences and metastases that had gone unseen. The researchers see possible uses before surgery, when checking for recurrence, and in future as a companion to a lutetium-based treatment that could target the same protein. The sources give no date for that. Arslan herself is cautious: it is "premature to claim that this agent represents a 'new molecular imaging standard'" until larger multicenter studies, stratified by subtype, confirm the results, and longer studies must show whether better staging translates into better outcomes.