Combined proteomics and metabolomics data of human RCC tissue was overlayed onto a stylized KEGG-based pathway diagram. Green, metabolite; orange, enzyme; black dot arrow, metabolism; red arrow, upregulated pathway; blue arrow, downregulated pathway; MAO, monoamine oxidase; DDC, dopa decarboxylase; ALDH, aldehyde dehydrogenase; IDO, indoleamine 2,3-dioxygenase; TDO, tryptophan 2,3-dioxygenase