Endometrial alterations in endometriosis: a systematic review of putative biomarkers

BACKGROUND: Endometriosis is usually diagnosed by an invasive procedure such as a laparoscopy. Great interest therefore lies in the potential to identify biomarkers which may be surrogates of disease presence or activity, especially relating to the effects of therapy. We have reviewed the existing literature on endometrial differences in women with endometriosis, and assess their potential use as disease biomarkers. METHODS: We used QUADAS (Quality Assessment of Diagnostic Accuracy Studies) criteria to conduct a systematic review of published papers over the past 25 years on the subject of endometrial differences in endometriosis. We searched for all studies assessing differences between eutopic endometrium of women with and without endometriosis. RESULTS: We identified 182 relevant articles that are summarized in the review. These studies assess over 200 potential biomarkers, including hormones and their receptors (n = 29), cytokines (n = 25), factors identified using proteomics (n = 8) and histological analysis (n = 10) of endometrial tissue. Sensitivity and specificity were reported or could be calculated for only 32 articles, and ranged from 0 to 100%. Of the nine highest quality studies, six identified putative biomarkers related to nerve fibre growth or cell cycle control, highlighting these areas as promising candidates for future biomarker research. CONCLUSIONS: This systematic review identified several reports of endometrial differences which have the potential to be biomarkers of endometriosis. However, larger studies in well-defined populations are clearly required to determine their true usefulness.