<h4>Background</h4>While the prognostic and predictive value of tumor cell-derived features such as grade, estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) status, and Ki67 index is well established in breast cancer, less is known about the prognostic role of tumor stroma. This evidence concerns the gene ESR1 and neoplasm.