Endometriosis Science: the full Synthesis

This short synthesis presents the main findings of the EndoSci project, which analyzes one century of scientific literature dedicated to endometriosis. For full information and context, you can access the following articles:

• Making sense of endometriosis? Exploring one century of scientific research (Introduction and Methodology)
• The Science of Endometriosis: a long and blurry history (Scope and Evolution)
• Research priorities in endometriosis science (Investigated Topics)
• The faces of endometriosis research (1/3): Nations (Countries)
• The faces of endometriosis research (2/3): Institutions (Specific organizations)
• The faces of endometriosis research (3/3): Gender (Female / Male researchers)

The long and blurry history of endometriosis

• Endometriosis “existed” in the distant past, even though it was not named, understood and identified as such by people and doctors.
• Conventional medical history typically considers that the modern identification of endometriosis starts with Rokitansky, who provided a microscopic description of the illness in 1860.
• Another canonical character that medical practitioners strongly emphasize is Sampson, who proposed a first theory of the (likely) mechanisms of the disease in the 1920s.
• The generalization of the diagnosis of endometriosis as such and its visibility are thus relatively recent by historical standards. In that sense, endometriosis was “invented” as a modern disease.
• At the beginning of the 20^th century, few publications were dedicated to endometriosis R&D. The scientific production focusing on endometriosis experienced its first period of substantial growth in the 1980s. However, the major increase can be identified from the 2000s onwards, with a jump from 556 yearly publications in 2000 to a total of 2000 in 2019.
• Before the mid-1980s, endometriosis-related research was experiencing slower growth than other scientific topics. However, in recent years, the number of publications dedicated to endometriosis has increased at either a similar pace or faster than for all scientific topics

• There seems to be an acceleration of endometriosis research linked to political activism centered on the disease in the 2020s. For instance, the US Congress has approved the doubling of funding for such research through the National Institutes of Health in 2020.
• Adequate funding levels are critical to scientific advances regarding endometriosis, as in other topics. They are also notoriously difficult to estimate, but it is possible to devise “guesstimates” – to be taken with a grain of salt.
• It is clear that the funding dedicated to endometriosis R&D has progressed in the last years, reaching about 150 million of 2020 euros in 2018. This is a significant improvement, about a doubling from the mid-1990s.
• Despite this progress, resources dedicated to endometriosis R&D at a global level remain limited. Arguably, regarding the prevalence of endometriosis, it is still too low. Global spending for endometriosis R&D is indeed comparable to the total economic output of small island nations such as Nauru or Kiribati, or smaller than the military budget of developing countries like Senegal. It also pales in comparison with R&D spending for other significant diseases, even when taking into consideration only US-funded R&D.

Research priorities, between key issues and fragmentation

• The biomedical sciences largely dominate endometriosis research, both historically and in recent years (98% of publications in the 2010s/2020s). This holds for all publications, but also for the most visible ones (as identified by their number of citations).
• In recent years, endometriosis research has become more diversified, with an increasing number of papers belonging to other scientific disciplines. This diversification could favor a better understanding of the multiple aspects of the disease, provided that the quality of these publications is high.
• Accordingly, multidisciplinary publications have increased, especially among the most visible ones.
• Based on the abstracts (i.e., detailed summaries) of publications, it is possible to distinguish different topics covered in the endometriosis scientific literature. Eight broad topics divided into 31 detailed topics are identified. These topics are presented in detail in a dedicated web application.
• Broad topics such as “causes and mechanisms of disease” and “treatment” largely dominate the scientific effort, both historically and presently. Other themes are less prevalent, but some interesting trends are notable. In the long run, the effort dedicated to “anatomy and classification” and “connections to other diseases” has declined in relative terms. It does not mean that fewer publications are released for these aspects, but their share tends to become smaller. These patterns hold true for all publications and the most cited ones.
• The evolution of detailed topics is more heterogeneous, including some changes within broad topics over time. For instance, genetics has experienced a recent surge. The trends for detailed topics can be explored using a dedicated tool (click here for most cited publications only).

• The most common symptoms of endometriosis are pain and infertility. However, evidence shows that there is an imbalance in the prioritization of these two issues in scientific publications. Indeed, more research is dedicated (specifically) to (in)fertility than to pain. This holds regardless of the period and when considering only the most cited papers as well. The reasons for this pattern are not clear (i.e., biases in researchers’ interests are not the only factor at play), but it should feed the debate on what is done and why.
• Clinical trials are studies focusing on developing healthcare innovations with direct applications for doctors and/or patients. As a result, they are critical to improving endometriosis care. According to Clinicaltrials.gov data, the number of endometriosis-related clinical trials has boomed since the 1990s.
• This development is exciting, as it shows a rise in interest to find solutions, including in the private sector. Moreover, the tested innovations are increasingly diversified, i.e., not only restricted to hormonal drugs or surgical procedures anymore.
• There is substantial potential and high expectations linked to these trials. However, it should be reminded that the failure rate of these studies is high and that media hype at too early stages can bring false hopes.

The faces of endometriosis research

Endometriosis research across nations

• Endometriosis research is heavily polarized in geographical terms: highly developed countries dominate the world output but also produce more visible research, i.e., accumulating more citations from other scientists.
• This situation persists when considering only the most recent research (i.e., published in the 2010s. It is also the case for citations), even though the rise of some emerging countries (in particular China) makes the domination of developed countries somewhat less extreme.
• In particular, the United States is the uncontested leader of endometriosis research, keeping its position over the years. Other major players include Italy, Japan, the United Kingdom and China.
• Big and wealthy countries thus dominate the bulk of endometriosis, but this merely reflects their potential to dedicate important resources to scientific advances in general rather than specific attention to endometriosis.
• Controlling for the size of countries can help us understand which truly prioritize the disease relative to others. In the 2010s, the number of endometriosis publications per capita was the highest in Belgium, Australia and Italy. By contrast, countries such as the USA or China were not major contributors compared to the potential granted by their large population.
• When considering the economic power of the different countries, smaller, less developed countries tend to rank higher in importance. They are indeed able to produce a relatively high number of endometriosis publications when compared to their economic output (GDP). Some developed countries such as Italy or New Zealand remain high for that metric as well.
• In any case, it is clear that a small number of countries still dominate the endometriosis R&D arena (e.g., USA, Italy, China, Japan…), with some of them (e.g., Belgium, Italy, Australia, New Zealand, Estonia…) emerging as players punching above their weight and genuinely prioritizing this disease across a set of different factors.
• There are specificities in the topics pursued by the different countries regarding endometriosis research. The most common topics can be defined as those with the highest abstracts’ share. The most specific topics refer to those with the highest level of overrepresentation. Many factors can influence the prioritization patterns at the national level.
•  For the broad topics, the most common ones (i.e., with the highest average share of the abstracts for the publications involving institutions based in the country) are overwhelmingly causes and mechanisms (48 countries) and treatment (63 countries). It is not surprising as they are the most common topics overall. Most specific broad topics are more diversified
• For the detailed topics, a few major ones tend to be the most common in several countries: “detailed description of specific subtypes” and “various or mixed biological mechanisms” are by far the most common, ranking first in 43 and 42 countries, respectively. By contrast, the level of fragmentation for the most specific detailed topics is very high.

Institutions rule? The contribution of specific organizations to endometriosis R&D

• At a more precise level, endometriosis research is carried out by a wide variety of institutions. However, educational and healthcare organizations largely dominate the landscape, as they encapsulate universities and hospitals, respectively.
• These institutions are spread out across the world (especially in developed countries) and exhibit diversified characteristics in terms of output, visibility, research priorities and gender balance of contributors.
• Some patterns can emerge from this variety. Healthcare institutions tend to dedicate slightly more effort to “anatomy and classification” in terms of covered topics, probably due to their surgical orientation. Similarly, education institutions tend to have a higher share of scientific output dedicated to “mechanisms and causes”, which also makes sense given the knowledge-oriented mission of universities. Companies tend to overperform in topics such as “mechanisms and causes”, “treatment” but at an even higher level “economic and health burden”. This is well-aligned to their attention on developing market applications for patients. Finally, Nonprofits are particularly concerned with “Symptoms and Daily life”.

Female disease, male science? The gender dimension of endometriosis

• As endometriosis is a gynecological disease, the gender dimension is crucial, both medically and socially. When it comes to scientific research, it is thus relevant to analyze the gender breakdown of involved scientists – and its potential influence on their work.  
• Historically, all scientific research and medicine have been dominated by males. This situation is also present in endometriosis research, with the overwhelming majority of researchers being men for an extended period. However, this situation has drastically improved over the course of the 20^th century, making endometriosis R&D a fading male bastion. Parity is probably almost reached, and the field could even be female-majority in the foreseeable future.
• Overall, most countries feature a male bias in the contributions to endometriosis R&D publications. However, this bias and its extent are subject to considerable variations. Some countries are almost gender-equal, and some even feature a majority of female contributions to endometriosis R&D (e.g., former Soviet countries).
• Recent publications show a gradual move towards a more gender-equal playing field in most countries.
• Zooming on specific countries such as France and the United States reveals that multiple factors are likely involved in the observed gender patterns (e.g., differences in access to studies, interests, working conditions, etc.). In particular, higher levels of feminization of science and medicine may not always result in higher levels of female contribution to endometriosis R&D. Simple extrapolations should thus be avoided.
• Can the overall male overrepresentation in endometriosis scientific publications have an impact on the produced knowledge? There are multiple channels through which an influence could be considered. A slight effect can be detected when looking at the linkages between the gender composition of teams and the topics covered in the publications. Indeed, some topics are more explored by male-dominated teams (e.g., anatomy and classification), female-dominated teams (e.g., symptoms and daily life) or gender-balanced teams (e.g., causes and mechanisms). However, in all cases, the effect is very small, suggesting a limited impact of the gender composition of teams on the studied topics in endometriosis research.
• This result obviously does not mean that gender has no impact on endometriosis research activities. For instance, qualitative effects can be expected regarding the types of formulated hypotheses, the type of evidence considered, or the existence of potential biases.

What is there to be done?

• After reviewing all this information, what could be done to improve the situation regarding endometriosis research?
• Support interest groups active in endometriosis awareness
• Lobby for an adequate level of funding for scientific research in general and for endometriosis in particular (e.g., by targeting members of government or parliament)
• Debate on research priorities for endometriosis research by involving patients and professionals
• Ensure high levels of ethics in human research on endometriosis to avoid the errors of the past
• Improve connections between research and healthcare to promote the diffusion of relevant findings