Importance of DNA repair pathways (a constituent part of DDR) in maintaining genomic instability and cancer etiology is highlighted in familial cancers with known high-penetrance germline mutations in DNA repair genes: BRCA1/BRCA2 in breast cancer, MMR and polymerase deficiency (MLH1, MSH2, MSH6, PMS2 and POLE genes) in CRC and ovarian cancers, deleterious mutations in RAD51C and RAD51D and BRCA1 mutation in ovarian cancers [20,21,22,23,24,25,26]. The gene discussed is MLH1; the disease is ovarian cancer.