In this prospective study reported by Gilbert and colleagues, the value of carbonic anhydrase IX (CA-9) expression in peripheral blood, as a surrogate marker of circulating tumor cells detected through an RT-PCR assay, is examined in 41 patients with clinically organ confined renal tumors prior to surgical extirpation.

Forty one patients had peripheral blood collected and assayed for CA-9 expression prior to surgical therapy. Median follow-up was 4.3 years and median patient age was 71 years. Pathologic analysis of the surgical specimens demonstrated 87.8% with renal cell carcinoma (RCC), 7.3% with oncocytoma, and 4.9% with angiomyolipoma. Of patients with RCC, 77.8% were clear cell, 16.7% were papillary, and 5.5% were chromophobe. Of the 41 patients, 68.3% were CA-9 negative in their peripheral blood, whereas 31.7% were CA-9 positive. Of the 13 patients that were CA-9 positive, 84.6% were clear cell RCC, 7.7% were chromophobe RCC, and 7.7% were oncocytoma. The 5 year disease free survival for patients that were CA-9 negative was 88.1% versus 39.5% in those that were CA-9 positive (p=0.048). Of the 28 patients that were CA-9 negative, 7.1% of patients demonstrated a tumor recurrence in follow-up. Of the 13 patients that were CA-9 positive, 30.8% demonstrated a tumor recurrence in follow-up.

This study suggests that assays of peripheral blood for CA-9 may be prognostic in patients with otherwise localized renal tumors. The significance of expression of CA-9 in benign tumor entities such as oncocytoma remains unclear. Clearly, establishment of this assay as a marker of prognosis in RCC awaits further, larger prospective studies.

Gilbert SM, et al., Urology 67(5): 942-945, 2006

Written by Christopher G. Wood, MD, a Contributing Editor with UroToday.

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