Preoperative identification of tumour type could have important implications for the choice of treatment for renal cancers. Antibody cG250 reacts against carbonic anhydrase-IX, which is over-expressed in clear-cell renal carcinomas. We aimed to assess whether iodine-124-labelled antibody chimeric G250 (¹²⁴I-cG250) PET predicts clear-cell renal carcinoma, the most common and aggressive renal tumour.

26 patients with renal masses who were scheduled to undergo surgical resection by laparotomy received a single intravenous infusion of 185 MBq/10 mg of ¹²⁴I-cG250 over 20 min in this open-label pilot study. Surgery was scheduled 1 week after ¹²⁴I-cG250 infusion. PET and CT scanning of the abdomen, including the kidneys, within 3 h before surgery was planned for all patients. The obtained images were graded as positive (defined as a tumour-to-healthy-kidney ratio >3 to 1) or negative for antibody uptake, and the surgeon was informed of the scan results before surgery. After surgery, resected tumours were histopathologically classified as clear-cell renal carcinoma or otherwise. The trial is registered on the clinical trials site of the National Cancer Institute website NCT00199888.

One patient received inactive antibody and was excluded from analysis. 15 of 16 clear-cell carcinomas were identified accurately by antibody PET, and all nine non-clear-cell renal masses were negative for the tracer. The sensitivity of ¹²⁴I-cG250 PET for clear-cell kidney carcinoma in this trial was 94% (95% CI 70–100%); the negative predictive value was 90% (55–100%), and specificity and positive predictive accuracy were both 100% (66–100% and 78–100%, respectively).

PET with ¹²⁴I-cG250 can identify accurately clear-cell renal carcinoma; a negative scan is highly predictive of a less aggressive phenotype. Stratification of patients with renal masses by ¹²⁴I-cG250 PET can identify aggressive tumours and help decide treatment.