Activation of both of the MAP and ERK pathways lead to increased levels of c-Fos and c-Jun, which are proto-oncogenes that are associated with high-grade lesions. Localization
Most often, endometriosis is found on the:

ovaries
fallopian tubes
tissues that hold the uterus in place (ligaments)
outer surface of the uterusLess common pelvic sites are:

vagina
cervix
vulva
bowel
bladder
rectumEndometriosis may spread to the cervix and vagina or to sites of a surgical abdominal incision, known as "scar endometriosis." Rectovaginal or bowel endometriosis affects approximately 5-12% of those with endometriosis, and can cause severe pain with bowel movements.Deep infiltrating endometriosis has been defined as the presence of endometrial glands and stroma infiltrating more than 5 mm in the subperitoneal tissue. The prevalence of DIE is estimated to be 1 to 2%. Deep endometriosis typically presents as a single nodule in the vesicouterine fold or in the lower 20 cm of the bowel. Deep endometriosis is often associated with severe pain. Extrapelvic endometriosis
Rarely, endometriosis appears in extrapelvic parts of the body, such as the lungs, brain, and skin. "Scar endometriosis" can occur in surgical abdominal incisions. Risk factors for scar endometriosis include previous abdominal surgeries, such as a hysterotomy or cesarean section, or ectopic pregnancies, salpingostomy puerperal sterilization, laparoscopy, amniocentesis, appendectomy, episiotomy, vaginal hysterectomies, and hernia repair.Endometriosis may also present with skin lesions in cutaneous endometriosis.Less commonly lesions can be found on the diaphragm or lungs. Diaphragmatic endometriosis is rare, almost always on the right hemidiaphragm, and may inflict the cyclic pain of the right scapula (shoulder) or cervical area (neck) during a menstrual period.
A 2004 review of studies of dioxin and endometriosis concluded that "the human data supporting the dioxin-endometriosis association are scanty and conflicting", and a 2009 follow-up review also found that there was "insufficient evidence" in support of a link between dioxin exposure and developing endometriosis. A 2008 review concluded that more work was needed, stating that "although preliminary work suggests a potential involvement of exposure to dioxins in the pathogenesis of endometriosis, much work remains to clearly define cause and effect and to understand the potential mechanism of toxicity". Pathophysiology
While the exact cause of endometriosis remains unknown, many theories have been presented to better understand and explain its development. These concepts do not necessarily exclude each other. The pathophysiology of endometriosis is likely to be multifactorial and to involve an interplay between several factors. Formation
The main theories for the formation of the ectopic endometrium-like tissue include retrograde menstruation, Müllerianosis, coelomic metaplasia, vascular dissemination of stem cells, and surgical transplantation were postulated as early as 1870. Each is further described below. Retrograde menstruation theory
The theory of retrograde menstruation (also called the implantation theory or transplantation theory) is the most commonly accepted theory for the dissemination and transformation of ectopic endometrium into endometriosis. It suggests that during a womans menstrual flow, some of the endometrial debris flow backward through the Fallopian tubes and into the peritoneal cavity, attaching itself to the peritoneal surface (the lining of the abdominal cavity) where it can proceed to invade the tissue as or transform into endometriosis.