A precursor of endometrial serous adenocarcinoma characterized by the replacement of the normal endometrial cells by malignant glandular cells that resemble the malignant cells of invasive serous adenocarcinoma. the endometrial neoplastic process is non-invasive. it may coexist with invasive endometrial adenocarcinoma or can be associated with metastases outside the uterus, in the absence of invasive endometrial carcinoma.