ONCOLOGY Vol 20 No 6_Suppl_5

The introduction of newer classes of chemotherapeutic agents, with varying mechanisms of action by which they affect tumor growth and viability, has challenged the traditional norms of clinical trial design and drug approval in oncology. Most notably, the emergence of cytostatic biologic agents with antitumor efficacy has necessitated reassessment of appropriate primary endpoints for phase II and III trials in advanced disease from both a clinical and regulatory standpoint. Recent data in the field establishes an endpoint hierarchy, which places progression-free survival (PFS) between overall survival (OS) and response rate (RR) as appropriate primary endpoints for assessing the clinical efficacy of cytostatic and cytotoxic agents.

Although improved survival is the "gold standard" for proving clinical benefit of oncologic therapy, the US Food and Drug Administration (FDA) has accepted significant results in clinical trials using surrogate endpoints as the basis for drug approval. One surrogate is the amount of tumor reduction, or tumor response. Although tumor shrinkage would seem to be a necessary precondition for improved survival, clinical studies of a variety of oncologic agents have not consistently demonstrated a correlation between the two in patients with renal cell carcinoma. Moreover, tumor response may not be an appropriate endpoint for evaluating the effects of the new targeted therapies, whose putative mechanisms are generally cytostatic rather than cytotoxic. Clinical trials suggest that some patients with other solid tumors, such as lung cancer, may derive clinical benefit from treatment that helps stabilize their disease. There is also controversy as to whether the Response Evaluation Criteria in Solid Tumors (RECIST) provides the most appropriate instrument for assessing tumor burden. Ultimately, use of a variety of endpoints as well as different trial designs may provide an adequate basis for investigating the benefits/risks of newer therapies.

This report of a case of cytokine-refractory metastatic, clear-cell renal cell carcinoma (RCC) presents some current issues related to use of targeted therapy in the community. Due to the different mechanisms of cytostatic vs cytotoxic agents, traditional response assessments may not always apply in deciding when to either continue or stop treatment. While community physicians may increasingly focus more on duration of response, symptom relief, and how well patients tolerate treatment, there is a clear need for validated surrogate markers of biologic activity and response, as well as randomized trials that directly compare some of the targeted therapies being applied in advanced RCC.

Several novel targeted agents are being tested for the treatment of advanced renal cell carcinoma (RCC), and results of phase I and II trials have been encouraging. A recently completed phase III, placebo-controlled study showed that median progression-free survival doubled from 12 weeks to 24 weeks in patients treated with the multi-kinase inhibitor sorafenib (Nexavar) (hazard ratio [HR], 0.44; P < .00001), and approximately three-quarters of patients had some degree of tumor regression. Furthermore, interim analysis showed an estimated 39% improvement in overall survival in sorafenib-treated patients (HR, 0.72; P = .018) and an investigator-assessed response rate of 10%, indicating that many more patients had clinical benefit than had tumor regression qualifying as response by traditional criteria. These data and others have added to the evidence of lack of correlation between response rate and clinical benefit in RCC patients (as well as in other tumor types) treated with targeted therapies. Issues surrounding study endpoints and biologic efficacy markers for molecular targeted agents in RCC are discussed in this article, with a focus on results of the Treatment Approaches in Renal Cancer Global Evaluation Trial (TARGETs).