Endometriosis is a mostly hidden disease that has doctors foxed.
One theory is that the cells involved, which mimic cancer but are not cancerous, migrate from the uterus and attach themselves to other parts of the body, where they continue to grow. Another suggestion is that they are not womb-lining cells but began as ones that later mutated because of an error in their genetic programming. This most commonly occurs in the ovaries, the ligaments supporting the uterus, the Fallopian tubes, the bladder and the bowel. The disease can very rarely occur in the lungs. Conventional diagnosis is difficult because even using a technique such as laparoscopy, in which the abdominal cavity is inspected through a fibre-optic tube inserted through a small incision at the navel, in many cases the endometriosis cannot be seen.