The endometrial hyperplasias revisited.

The proliferating lesions in the endometrium form a morphological continuum extending from benign to malignant, through a transitional pre-invasive stage. Within this spectrum, several classifications of endometrial hyperplasia have been developed over the years in which the precancerous lesions gained a substantial distinction, although not without inconsistencies in definitions and terminology. The revised WHO 1994 classification explicitly recognizes cytological atypia as the defining feature for distinguishing genuine hyperplastic lesions (simple and complex endometrial hyperplasia) from those that are potentially precancerous (simple and complex atypical endometrial hyperplasia) and puts an end to the verbal anarchy by adopting a common language of communication. This taxonomy, however, was criticized for complexity and low level of reproducibility. Thus, in the name of improved reproducibility a new classification was recently proposed which (a) combines simple and complex endometrial hyperplasia within one diagnostic category known as endometrial hyperplasia and (b) defines new criteria for recognising the precancerous lesions: a monoclonal growth, known as endometrial intraepithelial neoplasia (EIN), comprising clusters of crowded glands, greater than 1 mm in diameter, having a cytologically altered epithelium. The EIN concept was challenged of not being independently tested and received with great enthusiasm by some scholars and relative skepticism by others.