Invited Commentary: Endometrial Hyperplasia--Getting Back to Normal

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Abstract
Cancer precursors can help to reveal clues about how and when risk factors influence the development of carcinoma. Endometrial carcinoma is well-suited to studies of precursors: Strong risk and protective factors exist, as does a good candidate precursor lesion, called atypical endometrial hyperplasia. Atypical hyperplasia is the most severe type of endometrial hyperplasia, which ranges from mild, reversible proliferation to incipient carcinoma. In this issue of the Journal, Epplein et al. (Am J Epidemiol 2008;168:563–70) report that three established risk factors for endometrial carcinoma—obesity, parity, and smoking—are similarly associated with two types of endometrial hyperplasia: complex hyperplasia and atypical hyperplasia. How much these findings reveal about mechanistic pathways for endometrial carcinoma depends, in part, on three issues that specifically affect endometrial hyperplasia but also affect other precursors. They are: 1) potential misclassification of intermediate endpoints, 2) unsettled thresholds between low-risk and high-risk lesions, and 3) uncertain boundaries between normal tissue and early-stage precursors. In this commentary, the author explores how these issues might influence interpretation of the new data from Epplein et al. and shape future research on endometrial carcinoma precursors.