ATM and breast cancer: The second lumB-specific gene is APEX1. Genetic alterations in genes that code for proteins that play a role in DNA repair pathways and in homologous recombination of DNA such as APEX1, BRCA1, BRCA2, XRCC2, XRCC3, ATM, CHEK2, PALB2, RAD51, and XPD have been implicated in BC [40].