High-dose IL-2 produces a similar overall response rate to interferon-alpha, but approximately 5% of patients had durable complete remissions.[12,13,14,15,16,17] IL-2 has never been shown in a randomized controlled trial to result in longer survival. The current use of high-dose IL-2 mainly derives from the fact that it is the only systemic therapy that has been associated with inducing durable complete remissions, albeit in a small fraction (about 5%) of patients who are eligible for this treatment. The optimum dose of IL-2 is unknown. High-dose therapy appears to be associated with higher response rates but with more toxic effects. Low-dose inpatient regimens have activity against renal cell carcinoma with fewer toxic effects, especially hypotension, but have not been shown to be superior to placebo or any alternative regimen with regard to survival or quality of life. Outpatient subcutaneous administration has also demonstrated responses with acceptable toxic effects but, again, with unclear survival or quality of life benefit. Combinations of IL-2 and interferon-alpha have been studied, but outcomes have not been better with high-dose or low-dose IL-2 alone.[20,21]
Antiangiogenic and Other Targeted Therapy
A growing understanding of the biology of cancer in general, and renal cell carcinoma in particular, has led to the development and U.S. Food and Drug Administration (FDA) approval of six new agents targeting specific growth pathways. Two of the approved targeted therapies block the mammalian target of rapamycin (mTOR), a serine/threonine protein kinase that regulates cell growth, division, and survival.
Temsirolimus, an intravenously administered mTOR inhibitor, was shown to result in prolonged OS compared with interferon-alpha in a phase III randomized controlled trial that enrolled intermediate- and poor-risk patients. The trial enrolled patients with a variety of subtypes of renal cell carcinoma and was not restricted to clear cell kidney cancer. The HR for death was 0.73 (95% CI, 0.58–0.92, P = .008), making temsirolimus the only therapy for renal cell carcinoma to have clearly been shown to result in longer OS than interferon-alpha using conventional statistical analysis.
Everolimus is an orally administered mTOR inhibitor that was evaluated in a double-blind, randomized, placebo-controlled phase III trial. The trial enrolled patients with metastatic renal cell carcinoma with a clear cell component that had progressed during or within 6 months of stopping treatment with sunitinib or sorafenib, or both drugs. Median progression-free survival (PFS) was 4.0 months with everolimus compared with 1.9 months with placebo. No difference in OS was reported.
Based on research showing that most clear cell renal cell carcinomas carried a mutation resulting in constitutive production of cytokines stimulating angiogenesis, several agents that targeted vascular endothelial growth factor (VEGF)-mediated pathways were developed. Several of these agents have been shown in randomized controlled trials to significantly delay progression of clear cell renal cell carcinoma, but none has resulted in a statistically significant increase in OS as conventionally assessed. Many of these trials allowed crossover upon progression and, in some instances, other agents with similar biological activity were available to patients after they withdrew from the clinical trial. These facts may have made it more difficult to detect an OS benefit. For the clinician, this makes it challenging to determine the real benefit of these drugs to the patient. The four FDA-approved anti-VEGF agents include three oral tyrosine kinase inhibitors, pazopanib, sorafenib and sunitinib, and an anti-VEGF monoclonal antibody, bevacizumab. Axitinib is a newer, highly selective, and more potent inhibitor of VEGF receptors 1, 2, and 3 and has been approved by the FDA for the treatment of advanced renal cell carcinoma after the failure of one prior systemic therapy.