SFRP2 and nonpapillary renal cell carcinoma: Morris et al. described 38 genes methylated in ccRCC, among those only a small number was methylated with high frequency (≥50% of cases: APAF1, COL1A1, DKK2, DKK3, SFRP2, SFRP4, SFRP5, and WIF1) while rarely (<10%) in matched normal tissue (28).