ESR1 and breast cancer: With respect to somatic mutations, the Cancer Genome Atlas (TCGA) and Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) databases revealed that premenopausal (PreM) patients with breast cancer have greater numbers of mutations in 5 genes—CDH1, GATA3, MLL3, GPS2, and PI3KCA. Moreover, compared to post-menopausal (PostM) tumors, gene expression in PreM tumors is enriched in the integrin and laminin signaling pathways, EGFR signaling activation, and TGF-β, especially in estrogen receptor-positive (ER + ) breast cancer9.