Identification of a novel papillary renal cell carcinoma molecular subtype characterized by HIF-pathway over-activation

PurposePapillary renal cell carcinoma (pRCC), the second most common subtype of renal cancer, exhibits heterogeneity in molecular features and response to targeted therapies, including antiangiogenic drugs. Discovering molecular biomarkers able to stratify pRCC patients into clinically relevant subgroups and understanding the underlying mechanisms are urgently needed to advance precision medicine. Here, we molecularly dissect a large pRCC series through the expression of the targets of hypoxia inducible factors (HIF), master regulators of angiogenesis, metabolic reprogramming and immune microenvironment. Experimental DesignWe merged and analyzed multi-omic and clinical data of 346 patients derived from two pRCC series (TCGA-KIRP and a Spanish metastatic series). Altered pathways and differences in tumor microenvironment were identified through tumor transcriptomic analyses. Tumor metabolome analysis was performed in selected cases. ResultsMolecular revision of driver mutations classified 302 patients as pRCC, while uncovering misclassified cases. Analysis of HIF targets gene expression identified a subset of pRCC tumors with increased HIF activity (31%; "HIF-active"). These tumors were characterized by high hypoxia scores, increased angiogenesis, low expression of Krebs cycle genes and mitochondrial activity, high immune infiltration and increased epithelial-mesenchymal transition (P<0.0001; each feature) and they were associated with increased metastasis risk and worse overall survival (P<0.005). Metabolome analyses revealed that HIF-active tumors accumulated L-2-hydroxyglutarate (L-2-HG), an oncometabolite that leads to pseudohypoxia by inhibiting HIF prolyl hydroxylases and preventing HIF degradation. L-2-HG-accumulation agreed with diminished L2HGDH expression, associated with losing one copy of the gene and low expression of PPARGC1A, which regulates its transcription. ConclusionsHIF-pathway overactivation defines a pseudohypoxic pRCC molecular subgroup characterized by high angiogenesis, immune infiltration and aggressive features. These findings advance our understanding of pRCC diversity, revealing potential clues for the variable response of patients to targeted therapies and paving the way to more personalized pRCC treatments.