XRCC4 and cancer: DNA Damage Repair (DDR) genes: in the TCGA pan-cancer study, >80% of ACC samples displayed at least one DDR gene alteration including genes involved in: Mismatch Repair (MMR): MLH1-3, MSH2-6, PMS2; Homologous Recombination (HR): TP53BP1, BRCA1-2, BRIP1, RAD51, TOP3A; Damage Sensor (DS): ATM, ATR, CHEK2; Translesion Synthesis (TS): REV3L; Base Excision Repair (BER): POLB; other minor DDR gene alterations involve Direct Repair (ALKBH3, MGMT), Fanconi Anemia (FANCA, FANCD2) and Nonhomologous End Joining (LIG4, XRCC4, XRCC6) [19].