Carbonic Anhydrase IX Expression Predicts Outcome of Interleukin 2 Therapy for Renal Cancer

Purpose: Renal cancer response to interleukin 2 (IL-2) therapy and patient survival has been correlated with tumor histology and carbonic anhydrase IX (CAIX) expression. In an effort to confirm and expand these observations, we examined CAIX expression in pathology specimens from renal cancer patients who had previously received IL-2 therapy. Experimental Design: Paraffin-embedded tissue sections of renal cancer were immunostained with the MN-75 monoclonal antibody to CAIX and expression levels were correlated with histologic findings and clinical outcome. Results: Tissue specimens were obtained from 66 patients; 27 of whom (41%) had responded to IL-2–based therapy. Fifty-eight specimens were assessed as clear cell, with 56, 33, and 4 having alveolar, granular, and papillary features, respectively. Twenty-four (36%), 31 (47%), and 11 (17%) were classified into good, intermediate, and poor prognosis groups according to the Upton pathology model. Forty-one specimens (62%) had high CAIX expression. Twenty-one of 27 (78%) responding patients had high CAIX expressing tumors compared with 20 of 39 (51%) nonresponders (odds ratio, 3.3; P = 0.04). Median survival was prolonged ( P = 0.04) and survival >5 years was only seen in high CAIX expressers. In patients with intermediate pathologic prognosis, all nine responders had high CAIX expression versus 11 of 22 nonresponders. A resultant group with good pathologic prognosis alone or with intermediate pathologic prognosis and high CAIX contained 26 of 27 (96%) responders compared with 18 of 39 (46%) nonresponders (odds ratio, 30; P < 0.01) and exhibited longer median survival ( P < 0.01). Conclusions: CAIX expression seems to be an important predictor of outcome in renal cell carcinoma patients receiving IL-2–based therapy and may enhance prognostic information obtained from pathology specimens.