ESR1 and neoplasm: Thus the search for new prognostic biomarkers or testing the relevance of existing ones could contribute to therapeutic decisions complementing the traditional methods, including TNM (tumor, node, and metastasis) staging, tumor grade, and other clinicopathological features in addition to the use of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2/neu).