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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 3,900 Canadian women are diagnosed with cancer of the uterus, with 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 faster spreading.
The most important risk factor for endometrial cancer has to do with the hormone estrogen. Basically, high levels of estrogen increase the risk of endometrial cancer. Because cumulative lifetime exposure to estrogen is what counts, and older women are at much higher risk. Most endometrial cancers appear after menopause, and the risk continues to climb with each successive decade. About 95% of these cancers occur in women over the age of 40.
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, the greater the protective effect.
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 citrate*, a common medication for patients with breast cancer, has been thought to cause endometrial cancer in women who may be taking it to prevent the recurrence of breast cancer. However, the risk of recurrence of breast cancer without tamoxifen citrate in those women who are prescribed the medication is very much higher than the added risk of uterine cancer. If you are taking this medication, your doctor will arrange for regular monitoring to help detect early cancerous changes in the uterine lining.
Obesity is a strong risk factor. This is because fatty tissue in women produces large amounts of estrogen, and does so year-round, without a break. Overweight women are three to ten 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 in itself, while physical activity can be protective even without the added benefits losing weight may have.
People with a family history of this disease, and people in families with some types of inherited colon cancer or breast cancer may be at increased risk.
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.
At the same time, it's this symptom that allows the cancer to be detected early enough to get effective treatment. The Pap smear test, designed to find cancer in the cervix, often catches cancers located in the uterus, but it often misses them too.
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).
There's no screening test for endometrial cancer. It's true that these tumours are sometimes detected by the cervical Pap smear test (see cervical cancer), but this screening test is hit-and-miss when it comes to endometrial cancer; it merely catches endometrial cells that have been dislodged and swept down to the cervix. 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, usually performed in the physician's office, is the surest diagnostic procedure. Another method of tissue sampling is a D&C (dilation of the cervix and curettage, which is cutting of the uterine lining). However, a D&C requires anaesthetic, and may be unsuitable for a woman who is very elderly or frail. A transvaginal ultrasound is another procedure that may help diagnose this cancer, but the results are less certain than a biopsy.
The vast majority of uterine cancers are detected early when a woman notices abnormal vaginal bleeding and consults her doctor. Abnormal bleeding should never be ignored, especially in a postmenopausal woman. Taking estrogen supplements occasionally causes harmless abnormal uterine bleeding, but a doctor should always be consulted in any case.
A D&C obviously isn't appropriate for random or routine screening, but some high-risk women might want to consider getting the test done every year. Women at high risk would include those taking strong estrogen supplements that aren't balanced with progesterone, obese women, and above all women taking certain doses of tamoxifen, the breast cancer medication, which increases the risk of endometrial cancer by a factor of 5 to 12.
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 is confined to one location (low stage), and isn't an aggressive type (low grade), it's usually safe to stop treatment. Women with a slightly higher grade cancer or cancer at a more advanced stage usually require a course of radiation treatment after surgery to kill any remaining cancer cells.
In more widespread cancer, surgery isn't an option and radiation treatment is offered instead. Abdominal radiation treatment can have unpleasant side effects, including extreme nausea. Another common side effect is vaginal stenosis, in which the vagina begins to close up and requires regular stretching with a special device known as a dilator. This can be done at home. If the cancer is very advanced, chemotherapy is also used.
Synthetic progestins, a form of the hormone progesterone, are used to treat endometrial cancer when it is advanced or when it recurs. It has only mild side effects compared to typical cancer medications. There is no evidence that anyone has ever been cured by chemotherapy alone. Some women have been cured by radiation alone after deciding against hysterectomy. However, many experts agree that keeping the uterus intact reduces the chances of a cure.
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.
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