[The premalignant disease of the endometrium: endometrial intraepithelial neoplasia].

The WHO 1994 classification for endometrial hyperplasias is based on the morphologic features of the lesions. This system characterizes the nuclear cytologic morphology as typical or atypical and describes the glandular architectural pattern as simple or complex. The main problem of this classification is the poor reproducibility. Although the predictive value of the atypical category is high, there are many typical hyperplasia cases with cancer progression. Modern molecular data related to endometrial tumorigenesis and precise computerized morphometric analysis have identified the lesion that may be considered as a precursor of endometrioid adenocarcinoma. By definition, this endometrial intraepithelial neoplasia (EIN) is a clonal proliferation of architecturally and cytologically altered endometrial glands which are prone to malignant transformation to endometrioid (type I) endometrial adenocarcinoma. The morphometric basis of EIN diagnosis is the D-score (DS), which is a logical combination of three morphometric features that represent the glandular complexity, glandular volume and cytological alterations. PTEN inactivation and K-ras mutation are the earliest genetic changes that can be revealed in these lesions. Hyperplasia cases that do not fit into the EIN categories are considered as benign or hormonal endometrial hyperplasia. This is the theoretical basis of a new classification system in premalignant endometrial diseases. Retrospective clinical data proved the high predictive value of the EIN scheme, so the decision on therapy can be more established. The reproducibility is excellent with application of precise definitions and PTEN immunohistochemistry. In the "Blue book" published in 2003 the WHO introduces the new morphometric- and molecular-based EIN system, and recommends it as an alternative classification method.