SFRP2 and renal cell carcinoma: Previous studies have shown that promoters of most WNT antagonistic genes (sFRP1[28]–[30], sFRP2[31], sFRP3[32], sFRP5[33], DKKs[34], [35], and WIF1[36]) are methylated or epigenetically silenced in RCC, which results in uninhibited WNT signaling during cancer initiation or progression [26].