Cancer of the uterus is the most common cancer of the female reproductive organs. It's the fourth most common cancer among women overall, behind breast cancer, lung cancer, and colorectal cancer. Fortunately, it's also one of the most curable cancers.
Each year, about 7,200 Canadian women are diagnosed with cancer of the uterus. This cancer has a survival rate of over 80%. This figure is higher if the cancer is caught early.
19 out of 20 uterine cancers are cancers of the endometrium, the inner lining of the uterus. This is called endometrial cancer. The remaining 5% are tumours of the outer muscular lining, called sarcomas. In general, sarcomas are more aggressive and spread faster.
The most important risk factor for endometrial cancer has to do with the hormone estrogen. Estrogen stimulates the lining of the uterus (the endometrium) to grow. Women with high levels of estrogen in their bodies are at increased risk of endometrial cancer. Because cumulative lifetime exposure to estrogen is what counts, and older women are at highest risk. Most endometrial cancers appear after menopause, and the risk continues to climb with each successive decade. Over 90% of these cancers occur in women over the age of 45.
Obesity is a strong risk factor for endometrial cancer. This is because fatty tissue in women produces large amounts of estrogen, and does so continuously. Overweight women are 2 to 3 times more likely than average to develop endometrial cancer, depending on how much extra weight they carry and how long they have carried it. A diet high in fat can be a risk factor in itself. Physical activity can be protective even without the added benefits that losing weight may have.
Estrogen is produced in each menstrual cycle, and women who have had more menstrual cycles are at higher risk. This means that a 40-year-old woman whose first period came at age 11 is more likely to get an endometrial tumour than a 40-year-old who began menstruating at age 14. Since pregnancy interrupts these cycles, women who have had children are at lower risk than those who haven't. The more pregnancies a woman has had, the greater the protective effect. However, the number of menstrual cycles and pregnancies a woman has is a much smaller risk factor for developing endometrial cancer than the risk associated with obesity.
Estrogen supplements (or hormone replacement therapy, HRT), used to relieve the symptoms of menopause, may slightly increase the risk of endometrial cancer. However, estrogen is usually given in combination with another type of hormone called progesterone, which counteracts the effects of estrogen on the endometrium and negates the endometrial cancer risk. Oral contraceptive pills, in which the progesterone effect outweighs the small estrogen dose, even appear to offer some protection against endometrial cancer. Progesterone is the dominant hormone during a normal menstrual period. Therefore, younger women who don't menstruate normally (unless they're on the pill) are at higher risk of endometrial cancer.
Because of its estrogen-like effects, tamoxifen*, a common medication for patients with breast cancer, has been thought to increase the risk of endometrial cancer 3 to 5 times in women who may be taking it to prevent the recurrence of breast cancer for 5 years or longer. However, the risk of recurrence of breast cancer without tamoxifen in those women who are prescribed the medication is higher than the added risk of uterine cancer. If you are taking this medication, your doctor may arrange for regular monitoring to help detect early cancerous changes in the uterine lining.
People with a family history of this disease, and people in families with some types of inherited colon cancer, breast or ovarian cancer may be at increased risk.
People with diabetes and high blood pressure have a higher risk of developing endometrial cancer and often have poorer outcomes.
Symptoms and Complications
Endometrial cancer in its early stages has one predominant symptom: abnormal uterine bleeding. Bleeding is abnormal in a premenopausal woman if it occurs at unusual times. In a postmenopausal woman, any uterine bleeding is abnormal. One-third of postmenopausal women who see their doctor about abnormal uterine bleeding have endometrial cancer.
9 out of 10 uterine cancers cause bleeding. There are usually no other symptoms or warning signs in early endometrial cancer. More advanced uterine cancers can cause pelvic pain, weight loss, bloating and swelling of the abdomen (lower stomach area).
Making the Diagnosis
There's no screening test for endometrial cancer. The cervical Pap smear test (see the "Cervical Cancer" condition article), is not a screening test for endometrial cancer. Transvaginal ultrasound and endometrial sampling that are used for diagnosis (see below) are being studied for their value as screening tests.
The only reliable diagnostic test for endometrial cancer is a tissue biopsy (sample). Tissue sampling from the endometrium, called an endometrial biopsy, usually performed in the physician's office, is generally sufficient as the initial diagnostic procedure. Another method of tissue sampling is a D&C (dilation of the cervix and curettage, which is scraping of the uterine lining). However, a D&C requires anaesthesia, and may be unsuitable for a woman who is very elderly or has serious medical problems. A transvaginal ultrasound is another procedure that may help diagnose this cancer, but the results are less certain than a biopsy.
The majority of uterine cancers are detected when a woman notices abnormal vaginal bleeding. Abnormal bleeding should never be ignored, especially in a postmenopausal woman. Any woman over the age of 40 with abnormal vaginal bleeding should consult her doctor to help decide whether further testing is needed. Taking estrogen supplements occasionally causes harmless abnormal uterine bleeding, but a doctor should always be consulted in any case.
Treatment and Prevention
Removal of the uterus (hysterectomy) is essential to treat endometrial cancer. This won't interfere with sexual activity, but the operation leads to infertility and can't be reversed. Only after the uterus, fallopian tubes, and ovaries have been removed can doctors judge the extent of the cancer. If the cancer hasn't invaded deep into the wall of the uterus (early stage) and isn't an aggressive type (low grade), additional treatment may not be necessary.
In more widespread cancer, radiation, chemotherapy, or both may be offered instead of (or after) surgery. Women with tumours that have invaded further into the wall of the uterus or who have a higher grade cancer may require a course of pelvic radiation, chemotherapy, or both to kill the remaining cancer cells. Some women have been successfully treated using radiation alone after deciding against hysterectomy. However, most experts agree that keeping the uterus intact reduces the chances of successful treatment if there is no evidence of disease outside of the uterus at the time of diagnosis.
Pelvic radiation treatment can have side effects, including nausea, abdominal pain, and fatigue. Another common side effect of radiation of the pelvis is narrowing of the vagina (stenosis). This may make sexual intercourse difficult or painful. This may require regular stretching of the vagina with a vaginal dilator to allow for sexual activity, which can be done at home.
If the cancer is very advanced, chemotherapy may be used alone or in combination with radiation. Chemotherapy can cause many side effects. These side effects vary depending on what chemotherapy medications your doctor decides to give you.
Synthetic progestins, a form of the hormone progesterone, are sometimes used to treat endometrial cancer when it is advanced or when it recurs. Synthetic progestins have only mild side effects compared to typical cancer medications; however, the chance of success when treated by chemotherapy or progestins alone is low.