Cancer has been defined as a genetic disorder caused by the accumulation of genetic alterations, which result from various internal and external DNA damage that is left unrepaired. One of the main characteristics of cancer is a partial loss of DNA damage repair (DDR) pathway, resulting in increased DNA damage levels and replication stress. DDR inhibitors have been suggested as a new anticancer strategy, under the concept of synthetic lethality. The poly-(ADP-ribose) polymerase (PARP) inhibitor is the first DDR inhibitor to be used in clinical practice. PARP inhibitors have been tested in patients with BRCA1/2 germline mutations (gBRCA1/2mt) and shown robust clinical benefits in breast cancer with gBRCA1/2mt and serous ovarian cancer patients. The concept of synthetic lethality is not limited to gBRCAmt for PARP inhibitor, and discovering homologous recombination deficiency (HRD) markers beyond BRCA1/2 and identifying best candidates for DDR inhibitors are the active research areas. At the same time, various combinations of DDR inhibitors and other anticancer drugs are being tested in both preclinical and clinical studies. In addition, based on recent evidence of the immune-modulatory effect of PARP inhibitors, the combination of DDR inhibitors and immune checkpoint inhibitors is being actively investigated. Acquired resistance mechanism of DDR inhibitors, as well as defining best candidates and best combinations, would be future research topics for DDR inhibitors. Furthermore, it would also be crucial to establish a clinically relevant standardized method to detect HRD for future clinical use.
Keywords: BRCAness; DNA damage repair; Homologous recombination deficiency; PARP inhibitor; Synthetic lethality.