DKK1 and neoplasm: To date, four SFRP family genes (SFRP1, SFRP2, SFRP4 and SFRP5) and two DKK family genes (DKK1 and DKK3) have been identified as targets of epigenetic silencing in human tumours (Suzuki et al, 2002; Roman-Gomez et al, 2004; Lodygin et al, 2005; Aguilera et al, 2006; Niehrs, 2006).