Endometriosis (EM) is an estrogen-dependent disease characterized by the presence of epithelial, stromal, and smooth muscle cells outside the uterine cavity. It is a chronic and debilitating condition affecting ~10% of women. EM is characterized by infertility and pain, such as dysmenorrhea, chronic pelvic pain, dyspareunia, dysuria, and dyschezia. Although EM was first described in 1860, its aetiology and pathogenesis remain uncertain. Recent evidence demonstrates that the peripheral nervous system plays an important role in the pathophysiology of this disease. Sensory nerves, which surround and innervate endometriotic lesions, not only drive the chronic and debilitating pain associated with EM but also contribute to a growth phenotype by secreting neurotrophic factors and interacting with surrounding immune cells. Here we review the role that peripheral nerves play in driving and maintaining endometriotic lesions. A better understanding of the role of this system, as well as its interactions with immune cells, will unearth novel disease-relevant pathways and targets, providing new therapeutics and better-tailored treatment options.

Loss of protein BAF250a (ARID1A) expression is present in women with rectovaginal deep-infiltrating endometriosis (DIE) and endometriosis affecting the pelvic sentinel lymph nodes (PSLN). Partial loss of protein BAF250a was found in some of our patient samples, comprising all endometriosis entities, including rectovaginal DIE and endometriosis affecting the PSLN. Loss of BAF250a (BRG-associated factor 250a)/ARIDIA (AT-rich interactive domain 1A) protein expression was identified among endometriosis-associated ovarian carcinomas and ovarian endometriosis, and this phenomenon was described as a possible early event in the transformation of endometriosis into cancer. DIE affecting the bowel/rectovaginal site is the most aggressive presentation of endometriosis and its ‘risk’ of malignant transformation has not been studied so far. We evaluated the immunohistochemical expression of BAF250a protein in 70 samples from patients enrolled in this study who were surgically treated at a tertiary center, university Hospital. The samples submitted to investigation were from rectovaginal DIE (n= 25/30), endometriosis affecting the PSLN (n= 5/7), ovarian endometriosis (n= 20/20) and endometrium from patients without endometriosis used as controls (n= 20/20). Partial loss (i.e. in one tissue section some cells stained positive for BAF250a while other cells, usually an adjacent group, were negative) of BAF250a protein was identified in 36% (9/25) of rectovaginal DIE samples, 40% (2/5) of endometriosis lesions involving the PSLN, 30% (6/20) of endometriomas, and also in 25% (5/20) of endometrium from controls. We found no statistical correlation between occurrence of partial loss of BAF250a protein and the use or not of hormone medications (P = 0.106), cycle phase (P = 0.917) and stage of disease (P = 0.717). We only found partial loss of BAF250a protein expression, and in a small population of women, with relatively high frequency in all benign tissues assessed in the present analysis. Therefore, this finding alone should not be correlated directly with the risk of malignant transformation in these lesions. The occurrence of partial loss of BAF250a protein expression in women with rectovaginal DIE and endometriosis affecting the PSLN is described for the first time. The value of this finding as a predictor of malignant transformation in endometriosis must still be clarified and further studied in association with other molecular events, such as PTEN (phosphatase and tensin homolog) deletion and PIK3CA (phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha) mutation. We might then be able to identify in the future which patients with endometriosis are at higher risk of cancer. This study was supported by an internal Charité grant to the Endometriosis Research Center and the authors declare no conflicts of interest.