The replication process is regulated at multiple levels to ensure precise temporal control over the key events. First, pre-replication complexes (pre-RCs) assemble at thousands of DNA replication origins in late mitosis and G1 phase of the cell cycle. This is followed by replication initiation at the G1–S phase transition, where the DNA strand is melted by the MCM helicase and replicative polymerases precisely copy the DNA. To avoid over-replication of the genome, pre-RCs formation is strictly inhibited beyond G1 phase and only a subset of origins are activated during S phase. When replication is finished, TH 302 are in G2 phase where MCM helicase and DNA polymerases are unloaded from DNA. Recent insights have shed considerable light on how the replication processes can be challenged leading to replication stress (see below). However, certain regions of the genome, termed common fragile sites, are particularly difficult to replicate. They are sensitive readouts for replication stress because they are prone to DSBs following RS  and . In this review, we first discuss how DNA replication can be deregulated in cancer cell particularly at the level of replication initiation. Next, we consider cellular mechanisms dealing with such replicative stress as well as diseases associated with the deregulation of these mechanisms. Finally, we outline new therapeutic strategies that enhance replicative stress with potential to improve cancer treatment possibilities.