SFRP2 and renal cell carcinoma: Previous publications have demonstrated hypermethylation of many of these genes in RCC [16], [39]–[41], [43]–[47] and within the TCGA data the SFRP2, WIF1, DKK1 and DKK2 genes all had probes that demonstrated hypermethylation in greater than 15% of samples in one cohort.