SFRP1 and renal cell carcinoma: To review the current evidence on methylation markers in RCC, we previously performed a systematic review and identified GREM1, RASSF1A, GATA5, LAD1, NEFH, SCUBE3, PCDH8, SFRP1, and BNC1 as the most promising prognostic methylation markers for RCC at the moment [15].