In the present study, the gene expression dataset GSE55715, in which the gene expression of three various states, including healthy mammary epithelial cells, primary tumor cells from the right breast, and P7731 cell line (ER-/PR-/HER2-; triple negative bone metastasis breast cancer cell line) was characterized, is used for detecting the upregulated and downregulated genes in different breast cancer stages in the first step. This evidence concerns the gene ESR1 and breast cancer.