DKK1 and renal cell carcinoma: Increased methylation of probes for these two genes (DKK1, cg07684796; SFRP1, cg15839448) was observed in the methylated cluster 1 samples (Figure S3C), and hypermethylation of either of these genes correlated with poorer survival in ccRCC, PRCC, and ChRCC (p = 0.0015, p < 0.0001, and p = 0.0021, respectively) and in PRCC excluding the CIMP-RCC tumors (p = 0.0035) (Figures 3C and S3D).