Endometrial intraepithelial neoplasia

It is composed of a collection of abnormal endometrial cells, arising from the glands that line the uterus, which have a tendency over time to progress to the most common form of uterine cancer—endometrial adenocarcinoma, endometrioid type.

EIN lesions have been discovered by a combination of molecular, histologic, and clinical outcome studies beginning in the 1990s which provide a multifaceted characterization of this disease.

[2][3] The EIN diagnostic schema is intended to replace the previous "endometrial hyperplasia" classification as defined by the World Health Organization in 1994, which have been separated into benign (benign endometrial hyperplasia) and premalignant (EIN) classes in accordance with their behavior and clinical management.

The cells of an EIN lesion are genetically different than normal and malignant tissues, and have a distinctive appearance under the light microscope.

Diagnostic terminology is that used by pathologists, physicians who diagnose human disease by examination of histologic preparations of excised tissues.

All of the following diagnostic criteria must be met in a single area of one tissue fragment to make the diagnosis (Table III).