In women with pelvic pain or infertility, a high prevalence of endometriosis (from a low of 20% to a high of 90%) is reported (5,6). In women with unexplained subfertility with or without pain (regular cycle, partner with normal sperm), the prevalence of endometriosis is reported to be as high as 50% (7). In asymptomatic women undergoing tubal ligation (women of proven fertility), the prevalence of endometriosis ranges from 3% to 43% (8–13). This variation in the reported prevalence may be explained by several factors. First, it may vary with the diagnostic method used: laparoscopy, the operation of choice for diagnosis, is a better method than laparotomy for diagnosing minimal to mild endometriosis. Second, minimal or mild endometriosis may be more thoroughly evaluated in a symptomatic patient given general anesthesia than in an asymptomatic patient during tubal sterilization. Third, the interest and experience of the surgeon is important because there is a wide variation in the appearance of subtle endometriosis implants, cysts, and adhesions. Most studies that evaluate the prevalence of endometriosis in women of reproductive age lack histologic confirmation (8–10,14–19).
The following are identified risk factors for endometriosis: infertility, red hair, early age at menarche, shorter menstrual cycle length, hypermenorrhea, nulliparity, m¨ullerian anomalies, birth weight (less than 7 pounds), one of multiple fetal gestation, diethylstilbestrol (DES) exposure, endometriosis in first-degree relative, tall height, dioxin or polychlorinated biphenyls (PCB) exposure, a diet high in fat and red meat, and prior surgeries or medical therapy for endometriosis (20). Prior use of contraception or intrauterine device (IUD), or smoking is not associated with increased risk of endometriosis (21,22). Protective factors against the development of endometriosis include multiparity, lactation, tobacco exposure in utero, increased body mass index, increased waist-to-hip ratios and exercise, and diet high in vegetables and fruits (20). Some evidence suggests that women with a “pinpoint cervix” have an increased risk for endometriosis, but more studies are needed to confirm this observation (23).
Several publications link endometriosis with an increased risk for certain gynecologic and nongynecologic cancers (24,25). These associations are controversial and no data exist to inform clinicians regarding the best management of patients who might be at risk of developing such cancers (1). Endometriosis should not be considered a medical condition associated with a clinically relevant risk of any specific cancer (26). Data from large cohort and case-control studies indicate an increased risk of ovarian cancers in women with endometriosis. The observed effect sizes are modest, varying between 1.3 and 1.9 (27). Evidence from clinical series consistently demonstrates that the association is confined to the endometrioid and clear-cell histologic types of ovarian cancer (28). A causal relationship between endometriosis and these specific histotypes of ovarian cancer should be recognized, but the low magnitude of the risk observed is consistent with the view that ectopic endometrium undergoes malignant transformation with a frequency similar to its eutopic counterpart (29). Evidence for an association with melanoma and non-Hodgkin’s lymphoma is increasing but needs to be verified, whereas an increased risk for other gynecologic cancer types is not supported (28).
Although signs and symptoms of endometriosis were described since the 1800s, its widespread occurrence was acknowledged only during the 20th century. Endometriosis is an estrogen-dependent disease. Three theories were proposed to explain the histogenesis of endometriosis: 1.
Ectopic transplantation of endometrial tissue 2.
3.
The induction theory
No single theory can account for the location of endometriosis in all cases.