Non–clear cell renal cell carcinomas: Biological insights and therapeutic challenges and opportunities

The non–clear cell renal cell carcinomas (nccRCCs) are a diverse group of rare-variant renal carcinomas. Each subtype harbors a distinct cell of origin and exhibits a distinct clinical behavior and response to therapy. The advent of next-generation sequencing has drastically advanced our understanding of key genetic and epigenetic drivers in these tumors, although mechanistic studies are needed to elucidate pathogenesis. The only 2 randomized clinical trials in nccRCC included patients with diverse histologic subtypes. Both of these trials compared everolimus with sunitinib and provided evidence suggesting that frontline sunitinib is superior to everolimus in terms of progression-free survival. Renal medullary and collecting duct carcinomas do not respond to targeted agents, supporting the use of platinum-based chemotherapy as frontline therapy. Clinical evidence is currently emerging on the efficacy of c-MET inhibitors in patients with papillary type 1 RCC harboring germline c-MET mutations. Data on the activity of immune checkpoint inhibitors in this setting are lacking; however, several trials are ongoing in this space. The management of patients with nccRCC likely will improve in the future with histology-driven trials, which may pave the way for personalized therapies based on the molecular characterization of these orphan kidney cancer subtypes. Efforts must also be made to establish in vitro and animal models for testing hypotheses generated through extensive genomic analysis. Ultimately, collaborative national and international studies are urgently needed to improve therapeutic strategies in patients with metastatic disease.