Endometrial hyperplasia and progression to cancer: which classification system stratifies the risk better? A systematic review and meta-analysis.

Benign and precancerous endometrial hyperplasias (EH) are differentiated thorough two possible histomorphologic classifications: WHO (adopting the subjective evaluation of cytologic atypia) and EIN (adopting several histomorphologic parameters, evaluable subjectively, or objectively with a computerized analysis calculating a prognostic score, the D score). ACOG recommends the use of EIN system although no distinction was made between objective assessment (not widely available), and subjective assessment (more applicable in the common practice). Moreover, it is still unclear if subjective EIN system is actually preferable to WHO classification. We aimed to assess the reliability of WHO system, D score and subjective EIN system in stratifying the risk of progression to cancer in EH. MEDLINE, EMBASE, Web of Sciences, Scopus, ClinicalTrial.gov, OVID, Cochrane Library and Google Scholar were searched for relevant articles from the inception to August 2018. All studies assessing the rates of progression of EH to cancer were included. Twelve cohort studies and one case-control study, assessing 3629 EH, were included. Relative risk (RR) for cancer progression was calculated with 95% confidence interval (CI), and results were compared using Chi-square test (significant p value < 0.05). WHO system showed a RR of 8.74 (95% CI 6.66-11.47). Objective D score showed a RR of 29.22 (95% CI 13.24-64.51), significantly higher than WHO (p = 0.005). Subjective EIN system showed a RR of 19.37 (95% CI 5.86-64.01), intermediate between WHO and D score, without significant differences (p = 0.20 and p = 0.57, respectively). Objective EIN criteria with D score are significantly more reliable than WHO criteria in stratifying the risk of progression of EH to cancer. Subjective EIN criteria did not show significant superiority over WHO instead. Further studies are necessary to determine if subjective EIN system should replace WHO system in the routine diagnosis of EH.