Introduction
Endometriosis is one of the most common chronic gynaecological conditions, characterized by the presence of endometrial-like tissue that undergoes proliferation, bleeding and regeneration outside the uterine cavity (Mathew et al., 2016). Its prevalence in women of reproductive age is 2–10%, and is as high as 35–50% in women with pain and/or infertility (Baranov et al., 2015; Fassbender et al., 2015).
There are different theories of the possible causes of the disease but the exact mechanisms are still unknown. Treatment encompasses the removal of ectopic endometrial lesions by invasive surgery. Definitive diagnosis is currently made through surgical inspection and histological assessment of the removed endometriotic implants. However, the invasiveness of this diagnostic approach leads to the diagnosis often being delayed for many years, with an estimated average of up to 5–10 years (Soliman et al., 2017). Reducing the time to diagnosis would enhance the quality of life of affected women by making the available medical or surgical options more successful with earlier intervention. There is a strong international recognition that accurate minimally invasive diagnostic markers and more effective disease-modifying agents are needed for this commonly occurring disease (D'Hooghe et al., 2019; Rogers et al., 2017).
Women with endometriosis often present with other comorbidities, i.e. co-occurrence of one or more additional diseases. However, epidemiological data concerning the incidence of endometriosis and its comorbidity with various chronic conditions are often fragmented (Surrey et al., 2018), which adds even more complexity to the study of this co-occurrence. It seems that it could hold a strong relationship with complex immune disorders, since patients with endometriosis are at higher risk of autoimmune diseases, gynaecological cancers, asthma/atopic diseases, cardiovascular and inflammatory bowel diseases (Kvaskoff et al., 2015; Shigesi et al., 2019; Sinaii et al., 2002; Yuan et al., 2018). In fact, it is well known that endometriosis shares some characteristics with autoimmune diseases, such as Graves’ disease, polyclonal B-cell activation, abnormal function of T and B cells, inflammatory tissue damage (Yuk et al., 2016), altered immune surveillance or a heightened humoral immune response (Kvaskoff et al., 2015), and with ovarian cancer, such as invasion, unrestrained growth or neoangiogenesis (Samimi et al., 2019; Tarín et al., 2015). Altogether, these observations suggest that different diseases co-occurring with endometriosis could be genetically and clinically linked.
The objective of the present study was to identify the overlap between the molecular processes and biological functions underlying endometriosis and its comorbidities, which could explain the co-occurrence of these diseases with endometriosis and could lead to identification of potential specific biomarkers of this chronic disease.