Endometrioid adenocarcinoma is characterized by squamous, mucinous, or ciliated differentiation and presence of precursor lesion (endometrial intraepithelial neoplasia/atypical hyperplasia), and expression of ER and PR but it is negative for GATA-3 immunohistochemically. This evidence concerns the gene ESR1 and Endometrial Intraepithelial Neoplasia.