Several novel therapies have been approved recently in advanced renal cell carcinoma (RCC). These agents inhibit pathways downstream of loss of the von Hippel-Lindau gene VHL. They target the vascular endothelial growth factor (VEGF) ligand, VEGF receptor (VEGFR), mammalian target of rapamycin (mTOR), and other potentially important pathways. Even with improvements in survival, disease progresses in all patients. There is a critical need to increase complete responses (now rare). One such strategy is combining several agents to block different levels of the VEGF-VEGFR axis (vertical blockade). Alternatively, combination of a VEGF-VEGFR inhibitor with an mTOR inhibitor is attractive. Finally, horizontal blockade of VEGFR with epidermal growth factor receptor and/or platelet-derived growth factor receptor, all signaling pathways activated by hypoxia-inducible factor, is another approach. Already trials have revealed difficulties with combination therapy. By combining agents, the toxicity of 1 or both can be enhanced. The authors of this article report their experience with sorafenib plus bevacizumab, which produced increases in hand-foot syndrome, hypertension, and proteinuria, all known toxic effects. Clinical activity was impressive with 25 responses in 48 patients (52% response rate). Other combinations also required dose reductions (sorafenib with temsirolimus) or were intolerable (sunitinib with temsirolimus or sunitinib with bevacizumab). Unexpected toxicity characterized by microangiopathic hemolytic anemia occurred late in treatment with sunitinib and bevacizumab. Toxicity may be more severe in patients with RCC, who frequently have 1 kidney and poor renal function. Once tolerability for combination regimens has been established, it will be critical to design informative phase 2 trials and address the benefit of combination versus sequential therapy.
(c) 2009 American Cancer Society.