KMT2D and breast cancer: To understand when the known high‐frequency mutation genes of BC first appear in the progression of BRDC and how they drive progress, we mapped 18 high‐frequency mutations (TP53, PIK3CA, KMT2D, FAT3, ARID1A, GATA3, PREX2, APC, ERBB2, FAT1, CDH1, NOTCH2, PTEN, BRCA2, CIC, MAP3K1, AKT1, and AKAP9) (Figure 1C).