Given the critical role played by MRN in DDR and the interaction with several DNA repair proteins in multiple pathways1–3, we correlated MRN expression with other proteins involved in DSB repair (BRCA1, BRCA2, ATM, CHK2, ATR, Chk1, pChk1, RAD51, γH2AX, RPA1, RPA2, DNA-PKcs), RECQ helicases (BLM, WRN, RECQ1, RECQL4, RECQ5), nucleotide excision repair (ERCC1) and base excision repair (SMUG1, APE1, FEN1, PARP1, XRCC1, Pol β) in the breast cancer cohort. This evidence concerns the gene APEX1 and breast cancer.