Previously, we reported that MTH1 inhibitors TH588 and TH1579 selectively induce oxidative damage and kill Ras expressing or transforming cancer cells, as compared to non-transforming immortalized or primary cells. While this explains the impressive anti-cancer properties of the compounds, the molecular mechanism remains elusive. Oncogenes induce replication stress, re-sulting in under replicated DNA and replication continuing into mitosis, where TH588 and TH1579 treatment cause toxicity and incorporation of oxidative damage. Hence, we hypothesized that oncogene-induced replication stress explains the cancer selectivity. To test this, we overex-pressed c-Myc in human epithelial kidney cells (HA1EB), resulting in increased proliferation, polyploidy and replication stress. TH588 and TH1579 selectively kill c-Myc overexpressing clones, enforcing the cancer cell selective killing of these compounds. Moreover, the toxicity of TH588 and TH1579 in c-Myc overexpressing cells is rescued by transcription, proteasome or CDK1 inhibitors, but interestingly not by nucleoside supplementation. This suggest that cancer selectivity is unrelated oncogene-induced replication stress. We conclude that the molecular toxi-cological mechanisms how TH588 and TH1579 kill c-Myc overexpressing cells have several com-ponents and involves MTH1-independent proteosomal degradation of c-Myc itself, c-Myc driven transcription and CDK activation, and is likely unrelated to oncogene-induced replication stress.