Although a majority of endometrial tumors present with well-differentiated low grade endometrioid histology (Type 1), expressing high levels of estrogen and progesterone receptors (ER/PR) as well as epidermal growth factor receptor (EGFR), about one-quarter present as more advanced and aggressive tumors (Type 2), that are unlikely to be ER/PR-positive and have a much poorer prognosis. Here, ESR1 is linked to endometrium neoplasm.