Non-clear cell renal cell carcinoma narrative review: where we are in 2024.

Background and objective: Advances in non-clear cell renal cell carcinoma (RCC) have lagged behind clear cell RCC due to the heterogeneity and relative rarity of the disease. However, more advanced molecular and genetic testing has allowed us to gain a more detailed and nuanced appreciation of these malignancies. This has laid the foundation for the identification of the distinct mutational and molecular patterns such as succinate dehydrogenase (SDH)-deficient RCC, fumarate hydratase (FH)-deficient RCC, and translocation RCC, so that clinicians can create a more personalized approach to their clinical management. Particularly for the rare non-papillary RCC variant histologies, clinical trial representation is lacking. In the discussed studies, no histology enrolled more than 29 patients of any particular RCC aside from Papillary. As such, evidence-based management decisions can be challenging to make for this patient population.

Methods: We have collected the most up-to-date available evidence to describe the pathophysiology, molecular, and pathologic characteristics of the more commonly seen non-clear cell RCC variants, including papillary, chromophobe, translocation, FH-deficient, as well as a group of "unclassified" RCCs. Additionally, we provide an overview of the available evidence from recent clinical trials for non-clear cell RCC and current treatment paradigms.

Key content and findings: The diagnostic approach for renal malignancies is rapidly changing, favoring a more molecular and genetically based approach. These techniques will allow for a more detailed understanding of the clinical behavior of these cancers. Most data for non-clear cell RCC are from single-arm phase 2 clinical trials. The clinical response to vascular endothelial growth factor (VEGF)-tyrosine kinase inhibitors (TKIs) and immune checkpoint inhibitors (ICIs) varies greatly by histology.

Conclusions: Molecularly targeted therapy as monotherapy or when combined with immunotherapy have efficacy in non-clear cell RCC, though there are differences in treatment response by histology.