RB1 and breast cancer: This analysis confirmed the frequent mutation of genes, such as PIK3CA, TP53, GATA3, MAP3K1, RB1, and MLL3, which are known to be mutated in breast cancer and led also to the discovery of rare mutations involving genes, such as RUNX1, MYH9, TBX3, and CBFB. Particularly, PIK3CA mutations were observed in 16% of cases, MAP3K1 mutations in 15.5% of cases, and GATA3 mutations in about 9% of cases.