Eighteen patients with advanced renal cell carcinoma (RCC) were treated on a phase II trial with ZD1839 (IRESSA). Treatment efficacy was determined using the endpoint of improvement in time to progression (TTP) compared to TTP in patients who received interferon-alpha therapy. The Memorial Sloan Kettering Cancer Center database of renal cell patients shows that patients receiving therapy with interferon-alpha had a median TTP of 4.7 months, with 40% of patients having disease progression at 4 months. To show efficacy in this trial, 60% of evaluable patients would have to remain progression free at 4 months. Treatment with ZD1839 did not result in any complete or partial responses, and 13 patients (81%) had progression of disease within 4 months of start of therapy. At the dose and schedule used in this trial, the lack of antitumor activity associated with ZD1839 does not support further study in patients with metastatic RCC.