Background: Endometrial hyperplasia (EH) is a pathological condition which occurs due to unopposed estrogenic effect. It is usually manifest by abnormal uterine bleeding affecting women in 5th and 6th decades of life. Some cases of endometrial hyperplasia especially those with atypical cytological features may progress to endometrial adenocarcinoma, while others follow an indolent course. Several classification systems have been developed over years. Early classifications were based on structural and cytological features. However, the recently developed classification system by WHO in 2014 was based mainly on the cytological atypical features as the architectural features have been proved to be clinically irrelevant. Cellular morphology was also included in this classification system.
Conclusions: WHO 2014 classification system described both cellular morphology and nuclear atypia as some newly described variants like atypical mucinous glandular proliferation was proved to be precancerous despite of its minimal cytological atypia. Glandular architectural features were proved to be clinically irrelevant, so they were excluded from this classification.