Chromophobe RCC (ChRCC) was first described by Thoenes et al. in 1985 (Thoenes et al., 1985) and is the third most common subtype of renal cell carcinoma (RCC) behind clear cell RCC (ccRCC) and papillary RCC, representing about 5–7 % of renal cell carcinomas (Moch et al., 2022, Henske et al., 2023). It arises from α-intercalated cells, a mitochondria-rich population of cells in the distal nephron (Schaeffeler et al., 2019, Skala et al., 2020, Zhang et al., 2021a, Chen et al., 2022, Labaki et al., 2025). ChRCC exhibits a characteristically low tumor mutational burden and lacks well-defined driver mutations, with TP53 being the most frequently mutated gene in approximately thirty-two percent of patients, while forty percent of tumors lack identifiable oncogenic driver (Davis et al., 2014, Niknafs et al., 2023). Whole chromosomal losses affecting chromosomes 1, 2, 6, 10, 13, 17, and 21 are common (Ohashi et al., 2019, Kovacs et al., 1992), and chromosomal re-duplication leading to a hyperploid state is associated with metastasis and dedifferentiation into the aggressive sarcomatoid subtype (Kapur et al., 2024). The cytoplasm of ChRCC cells shows marked accumulation of abnormal mitochondria with frequent mitochondrial DNA mutations, and ChRCC exhibits the highest expression of 13 mitochondrial DNA genes in The Cancer Genome Atlas (TCGA) (Davis et al., 2014, Yuan et al., 2023, Rathmell et al., 2015).

While most patients present with organ-confined disease (Casuscelli et al., 2019), significant therapeutic challenges emerge once metastasis develops: median overall survival (OS) is 27 months (Kroeger et al., 2013), and – unlike ccRCC – ChRCC shows inconsistent response to tyrosine kinase and immune checkpoint inhibitors (Voss et al., 2014, Hutson et al., 2021a, Zarrabi et al., 2021). ChRCC has traditionally been included into broad RCC trials or into “non-clear cell” (nccRCC) trials, obscuring histology-specific efficacy signals and holding back the development of effective and specific therapeutic regimens.

The past few years, however, have witnessed an inflection point driven by prospective ChRCC-enriched studies, deeper biologic interrogation, and growing patient-advocacy momentum. Recent single-cell transcriptomic and T-cell receptor profiling (Labaki et al., 2025) has shown that ChRCC upregulates genes involved in ferroptosis defense, mTORC1 signaling, and the IL-15 pathway, while downregulating HLA-A, -B and -C, consistent with impaired antigen presentation. In addition, the microenvironment appears to be markedly “immune-cold”: CD8⁺ T-cells constitute only about 10 % of immune infiltrates, lack classical exhaustion markers (PD-1, CTLA-4, LAG-3, TIM-3, TIGIT), and show minimal clonality – suggesting bystander rather than tumor-specific activity. The biological features correlate with clinical outcomes: in the International Metastatic RCC Database Consortium, first-line immune-checkpoint inhibition yielded an objective response rate of only 12 % in metastatic ChRCC, four-fold lower than ccRCC. By contrast, VEGF-tyrosine kinase inhibitors (TKIs) and mTOR inhibitors seem to achieve survival outcomes comparable to ccRCC, suggesting that immune exclusion, rather than intrinsic drug resistance, underlies the selective failure of immune checkpoint inhibitors (ICIs).

Progress is now culminating in ChRCC-inclusive trials evaluating a KIT-targeted antibody-drug conjugate (ADC) and Natural Killer (NK) adoptive cell therapy, offering a long-awaited path toward therapeutic breakthroughs.