MMP9 and nonpapillary renal cell carcinoma: For preliminary exploring the mechanism behind the different roles of the four genes in ccRCC, the PPI network that were centered on each of the four genes including MMP9 (Fig. 6A), IRF7 (Fig. 6C), NFKB1 (Fig. 6E) and HMOX1 (Fig. 6G) were constructed, followed by GO/KEGG analyzing the biological functions as well as signaling pathways the fours genes and their surrounding partner genes most enriched.