SIRT1 and malignant colon neoplasm: Finally, down-regulation of SIRT1 in breast and colon cancer cell lines leads to re-expression of the Wnt pathway inhibitors, SFRP1 and SFRP2 (Secreted Frizzled-like Proteins 1 and 2), which are frequently inactivated in human cancers through epigenetic means [24], as discussed in greater detail below.