Anti-cancer activities of existing drugs shown in this study cover diverse mechanisms such as inhibition of mTOR and VEGFR2 signaling, PI3K/Akt signaling inhibition, COX and selective COX-2 inhibition, NF-κB inhibition, Wnt/β-Catenin pathway inhibition, DNMT1 inhibition, GSK-3β inhibition, suppression of anti-apoptotic proteins, tyrosine kinases and some growth factor inhibition, HIF-1α suppression, tumor angiogenesis reduction, and matrix metalloproteinases enzyme inhibition to resist invasion and metastasis (Figure 4). This evidence concerns the gene DNMT1 and cancer.