MSH2 and breast cancer: Key genes involved in BC with high TMB include TP53, KMT2D, KDM6A, ARID1A, KMT2C, PIK3CA, FAT4, EP300, and RB1. Additionally, some of the MMR (MSH2, MSH6), DDR (ATM, BRCA2, POLQ, CDK12, ATR, BRIP1), and polymerase-encoding genes (POLE, POLD1) are frequently altered in TMB high tumors (59, 60).