CBX4 and nonpapillary renal cell carcinoma: Moreover, given the important role of promoter methylation in the process of renal tumors, we used UALCAN to investigate the promoter methylation levels of CBXs in ccRCC and found that the promoters of CBX2, CBX3, CBX4, CBX5, CBX6, CBX7, and CBX8 were hypermethylated in ccRCC tissues, while the CBX1 promoter was hypomethylated in ccRCC tissues, compared to those in the normal kidney tissues (Figure 7).