NKD2 and brain cancer: Interestingly, the expression of several genes in the KEGG pathway “pathways in cancer”, such as ptk2, kit, lpar1, notch1, rasgrp4, ifngr1, ptch1, apaf1 and dll1, and Wnt pathway-related genes, such as wif1, rspo3, nkd2, sfrp1, smad3, wnt7a, wnt7b and axin1, showed opposite expression patterns between brain regeneration and brain cancers, suggesting that these genes may play key roles in preventing the cells from undergoing carcinogenesis (Figures 7A,B).