DKK1 and colorectal cancer: There is evidence showing that vitamin D treatment is negatively correlated with promoter methylation status of the adenomatous polyposis (APC) gene, a tumor suppressor gene in colorectal cancer [375], as well as dickkopf-related protein 1 (DKK1) [376], E-cadherin [377], PDZ-LIM domain-containing protein 2 (PDLIM2) [378] and p21 [379].