Considering the classification of endometrial hyperplasia

E ndometrial hyperplasia is a common disease (at least 120 000 new cases each year in the European Union). The wide range of histological presentations of endometrial hyperplasia is accompanied by high intraobserver and interobserver variability in diagnostic classification. The overall risk of progression of hyperplasia to cancer is 5–10%, but this may vary substantially between individual patients according to the histological pattern. Unreliable diagnosis of hyperplasia translates into inappropriate treatment, either as a result of the undertreatment of high risk lesions or the overtreatment of low risk lesions, which leads to unnecessary suffering and high treatment costs. Many different classification systems for endometrial hyperplasia have been proposed and used over the past few decades. Before 1985, such terms as ‘‘mild, moderate, and severe hyperplasia’’ were often used in the USA, whereas ‘‘cystic’’ and ‘‘adenomatous hyperplasia’’ was more fashionable in Europe. By 1982, confusion in terminology and disagreement in criteria between experts, even within the same country, became painfully clear. 2 In 1994, the World Health Organisation proposed its classification for endometrial hyperplasia (WHO94). This was based upon a seminal study, which correlated the presence of cytological atypia with heightened cancer risk, and had the effect of standardising terminology world wide. The WHO94 classification uses two criteria: glandular complexity and nuclear atypicality. This resulted in four categories: simple (SH), complex (CH), simple atypical (SAH), and complex atypical hyperplasia (CAH), which have different progression risks of ,1%, 3%, 8%, and 29%, respectively.