Is endometriosis a preneoplastic condition?

Endometriosis is a condition that is characterized by the presence of endometrial tissue implants that are outside the uterine lining. It is presented in 10–15% of women in the reproductive age group, 2–5% of postmenopausal women, 25–30% of infertile women and 40–70% of women with chronic pelvic pain. The natural course of endometriosis starts with ectopic tissue implantation and bleeding occurs in this ectopic tissue. In this area, inflammation and fibrin deposition are seen. The final results of these events are adhesion, scar formation and distortion of peritoneal surfaces. In 1925, Sampson firstly described a case with an ovarian carcinoma derived from an endometriotic lesion [1]. Since then, many retrospective studies have documented an increased rate of endometriosis in women with ovarian cancer, especially ovarian cancer with endometrioid adenocarcinoma and clear cell carcinoma. It has been understood that there are many histological, molecular and genetic alterations in the ectopic endometrial tissue. There are two pathways in the course of human endometriosis. The first and usual pathway is that ectopic endometriotic tissue on the ovarian surface encounters an unfavorable microenvironment and progresses regression with scar formation. However, the second and unusual pathway is that endometriotic tissue encounters a favorable microenvironment and continues growth to form endometriotic cysts/masses. This evolution causes an increased risk of accumulating additional genetic alterations that may lead to the development of ovarian cancer. The relationship between endometriosis and cancer is an important matter. The points of discussion in this article are to clarify whether endometriosis should be considered a precursor lesion of cancer such as ovarian, uterine and mammary cancer.