The need for a universal endometriosis classification

A literature search revealed there is no international agreement on how to characterize or classify endometriosis.

The search in the Journal of Minimally Invasive Gynecology also concluded that most classification/staging systems show little to no correlation with patient outcomes.

The search, which was limited to PubMed and MEDLINE, and English language studies published from inception in 1966 to August 2020, comprised 70 studies that either described a classification, staging, or reporting system in endometriosis (n = 24) or evaluated 1 (n = 46). A total of 22 endometriosis classification-staging-reporting systems were assessed.1

The studies highlighted a discrepancy between the intended and the evaluated purpose. There is also a general lack of validation data confirming a correlation between pain symptoms or quality of life to any of the current systems.

A few studies, though, confirm the value of the Enzian system for surgical description of deep endometriosis. Also, the endometriosis fertility index (EFI) has been validated for its intended purpose of predicting the probability of natural conception after surgery. However, the EFI system needs further evaluation of the importance of the different parameters and whether to include the completeness of surgical treatment.

The revised American Society for Reproductive Medicine (rASRM) system has also been evaluated, but often with negative conclusions.

Apart from rASRM, Enzian, and EFI, only 2 other classification systems have been evaluated for their intended purpose: the ultrasound-based endometriosis staging system (UBESS) and the disease extent, complaints, objectives (ECO).

“This overview of existing systems is a first step in working towards a universally accepted endometriosis classification,” wrote the authors, who acknowledged that endometriosis is a challenging disease to classify because it has different phenotypes and presentations for the type of lesions and their location. The disease also has various symptoms without a clear connection to phenotype or presentation.

Furthermore, the natural progression of endometriosis is unknown.

Despite these roadblocks, there appears to be a need for a validated classification or descriptive system for endometriosis to support further progress in defining subgroups. More significant, though, is that such a system could guide therapeutic options for women with pain and/or infertility.

System conformity would also assist endometriosis research by unifying patient subgroups and enhance the development of prognostic and predictive tools.

“Classification and staging systems are widely used in medicine and have been shown to be valuable in guiding clinical management,” wrote the authors, including the American Joint Committee on Cancer tumor-node-metastasis (TNM) staging systems for cancer, which was developed in the early 1950s to guide clinical classification of cancer cases by anatomical extent.

The TNM system, which is revised every 6 to 8 years, is now in its eighth edition and includes a summary staging or classification linked to prognosis and used for treatment planning.

The TNM system has also been increasingly complemented by molecular marker data that more accurately stratifies risk in patients and guides appropriate treatment options.

The longevity and update systems applied to TNM staging, plus the additional molecular subtype identification, are probably salient guides for the design of future endometriosis classification and staging systems that correlate with relevant patient outcomes, according to the authors.

Meanwhile, the goal and purpose of published classification, staging or reporting systems for endometriosis are often ignored when assessing classification or staging systems, thus limiting the value of the evaluation studies and of the systems in general, according to the authors.


  1. Vermeulen N, Abrao MS, Einarsson JI, et al. Endometriosis classification, staging and reporting systems: a review on the road to a universally accepted endometriosis classification. J Minim Invasive Gynecol. 2021. 28(11):1822-1848. doi:org/10.1016/j..jmig.2021.07.023