Immune checkpoint blockade as a novel immunotherapeutic strategy for renal cell carcinoma: A review of clinical trials

Renal cell carcinoma (RCC) is a common genitourinary malignancy; when metastatic, it is almost uniformly fatal. For many years non-specific immunotherapy was the mainstay of treatment for metastatic RCC, but led to only modest success and significant side-effects. More recently, seven targeted therapy drugs have been approved to treat metastatic RCC; these drugs impede RCC cell growth, proliferation, and angiogenesis and have had a significant impact on patient outcomes, but with infrequent long term responders. Thus, a renewed emphasis on immunotherapy has emerged over the last several years with the development and testing of a novel class of immunotherapeutic agents called checkpoint inhibitors. These drugs have targeted the programmed cell death 1 (PD-1) and cytotoxic leukocyte antigen 4 (CTLA-4) pathways on regulatory T cells, leading to immune response enhancement and immune-mediated anti-tumor effects in multiple malignancies, including RCC. A number of studies recently reported utilizing checkpoint inhibitors, either alone or in combination with other checkpoint inhibitors or vascular endothelial growth factor targeting agents, and these studies have shown significant and at times durable responses in RCC patients. This has led to the development of further phase I, II, and III trials and this review will discuss the history and currently available data for immune checkpoint blockade in RCC.