ESR1 and breast cancer: Herein, we performed a meta-analysis of public available breast cancer gene expression omnibus (GEO) datasets to further detect the differential expression of EYA2 in normal vs. breast tumors, and to explore the association between EYA2 and tumor differentiation, the status of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) as well as molecular subtypes at mRNA level.