- Interleukin-2 (IL-2) has some antitumor activity in patients with renal cell carcinoma. It has been noted that response to IL-2 and prognosis may be adversely affected by elevated serum levels of C-reactive protein (CRP) or interleukin-6 (IL-6). We used thalidomide to treat patients with cancer-induced cachexia and noted that the drug significantly reduced serum levels of CRP and IL-6 to normal or near normal levels in a substantial fraction of patients. We tested whether thalidomide might potentiate the response of patients with renal cell carcinoma to IL-2. Four patients with metastatic renal cell carcinoma and high serum levels of CRP and IL-6 who had experienced disease progression on IL-2 were retreated with the same IL-2 regimen combined with thalidomide 300 mg p.o. daily. Two patients achieved good partial responses and 2 patients had prolonged disease stabilization with the combination of IL-2 plus thalidomide. The regimen was well tolerated without increased IL-2-associated toxicity. Reduction of serum CRP or IL-6 levels with thalidomide may enhance the responsiveness of renal cell carcinoma to IL-2. A Phase II study of the combination is in order. It is possible that the thalidomide-induced normalization of serum acute phase proteins might improve the response of other types of malignancy to IL-2 or other immune-based therapies. © 2004 Wiley-Liss, Inc.