COL4A2 and nonpapillary renal cell carcinoma: Recently, Cheng et al. 20 have identified 5 complement-related genes (A2M, APOBEC3G, COL4A2, DOCK4, and NOTCH4) through a comprehensive analysis of mRNA expression data in the database of the International Cancer Genome Consortium, and established a risk score model to predict the prognosis of ccRCC.