ESR1 and breast cancer: The Cancer and Genome Atlas Project (TCGA) reported a high frequency of TP53 (37%) and PIK3CA (36%) mutations in breast cancer patients.[11] TP53 mutations were seen in the majority of basal-like cancers (80%), which is comprised mainly of TNBCs, and only in a minority of patients with Luminal A cancers (12%), which are strongly ER-positive tumors of low grade.