How is Endometriosis Different from Endometrial Cancer?

Endometriosis is a non-cancerous disorder that occurs when tissue lining the inside of the uterus, known as the endometrium, appears in other parts of the body. It usually is found in the lower abdomen or pelvis but can appear in virtually any organ or tissue. Endometrial cancer, by contrast, occurs when cells in the endometrium begin to grow abnormally, forming a solid mass and potentially spreading elsewhere in the body.

Endometriosis is a fairly common condition, affecting three to 10 percent of reproductive-age women. Endometrial cancer, though it affects far fewer women, is the most common gynecological cancer in the United States. The two diseases tend to arise at different stages of life: most women diagnosed with endometriosis are in their 30s and 40s; the average age for diagnosis of endometrial cancer is 62, and it is fairly rare in women under 45.

Panos Konstantinopoulos, MD, PhD, works on endometrial cancer research at Dana-Farber.
Panos Konstantinopoulos, MD, PhD, works on endometrial cancer research at Dana-Farber.

The most common symptom of endometriosis is pain, often in the lower abdominal area or pelvis and during menstruation. This is because endothelial tissue, wherever it is located, breaks apart and bleeds at the end of the menstrual cycle. If the bleeding occurs outside the uterus, the blood may build up in surrounding tissue and cause painful swelling or inflammation. Endometriosis can also result in scar tissue, which adds to the pain.

Other symptoms of endometriosis include decreased fertility, painful bowel movements, bloating, constipation, blood in the urine, pain on urination, and, sometimes, vaginal bleeding.

Some of the symptoms of endometrial cancer mirror those of endometriosis. The most common symptom is vaginal bleeding, which is present in 90 percent of women at the time of diagnosis. Many of the other symptoms aren’t specific to endometrial cancer and can result from a wide range of conditions.

As endometrial tumors grow in size, they can produce a variety of problems including pelvic or back pain, painful urination, painful sexual intercourse, blood in the stool or urine, and weight loss.

To diagnose endometriosis or endometrial cancer, doctors perform a biopsy. For endometriosis, this entails a laparoscopy, in which a surgeon views the intra-abdominal and pelvic areas with a camera mounted on a thin, flexible tube and collects a sample of suspected endometrial tissue. For endometrial cancer, the tube is passed into the uterus through the vagina to collect a tissue sample. Examination of the tissue by a pathologist determines if disease is present.

For endometrial cancer, pathologic examination may also indicate what subtype it is, how aggressive it is, and whether it has invaded surrounding tissue. Another technique for diagnosing endometrial cancer is a transvaginal ultrasound, which uses sound waves to gauge the thickness of the endometrium, which can help doctors distinguish between benign and malignant causes of bleeding.

Treatment for endometriosis can include medications to alleviate the pain associated with the disease. Since the growth of endometrial tissue is often driven by hormones, hormone-blocking agents be prescribed as well. Surgery may be used to remove or burn away endometriosis tissue outside the uterus, and to remove scar tissue that may have displaced the fallopian tubes and ovaries.

Treatment for endometrial cancer depends on a variety of factors, including the subtype of the cancer, its extent within the body, aggressiveness, responsiveness to hormone-blocking drugs, and other medical conditions a patient may have. The vast majority of patients undergo surgery to determine how extensive the cancer is and to remove as much of the tumor as possible. Many also receive radiation therapy to reduce the chances that the cancer will come back. Tumors whose growth is fueled by hormones are often treated with hormone-blocking agents. And patients whose cancer has spread beyond its initial site are likely to receive chemotherapy to kill cancer cells dispersed throughout the body.

As a general rule, having endometriosis is not associated with the development of endometrial cancer or of an increased risk of cancers in general. (Some rare types of ovarian cancer, such as clear cell ovarian cancer and endometrioid ovarian cancer, are more common in women with endometriosis, but the risk is very low ­– under one percent). When endometrial cancer does occur in a woman who has, or once had, endometriosis, it tends to arise at a later age and is highly treatable. A study published in 2017 that involved well over 100,000 women found that endometriosis was not strongly linked to endometrial cancer, and concluded that the two diseases develop by markedly different biological routes.