PDCD1 and colorectal carcinoma: As an LRP5/LRP6 receptor-binding protein that inhibits Wnt/β-catenin pathway activity, Dickkopf (DKK) has a therapeutic effect on CRC with aberrant activation of the Wnt/β-catenin pathway (68), and the team of Sui (69), in an MSI/dMMR CRC PDO-based study, observed that DKK1 inhibited the activity of PD-1 inhibitors, mainly by limiting the immune function of CD8+ T cells and increasing tumor cell activation.