What is cancer of the uterus?
Cancer of the uterus begins from abnormal cells in the lining of the uterus (endometrium), the muscle tissue (myometrium), or the connective tissue supporting the endometrium (stroma).
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The uterus, or womb, is part of the female reproductive system, which also includes the ovaries, fallopian tubes, cervix (neck of the uterus) and vagina (birth canal).
The uterus is about the size and shape of a hollow, upside-down pear. It sits low in the abdomen between the bladder and rectum, and is held there by muscle. It is joined to the vagina by the cervix, which is the neck of the uterus. The uterus is where a foetus grows during pregnancy. It is made up of two layers:
- Myometrium – the outer layer of muscle tissue. This makes up most of the uterus.
- Endometrium – the inner layer or lining. In a woman of child-bearing age, the hormone oestrogen causes the endometrium to become thicker each month to prepare for pregnancy.
Each month, the ovaries release an egg (ovum) in a process called ovulation. The egg travels down the fallopian tube into the uterus. If the egg is fertilised by a sperm, it will implant itself into the lining of the uterus and grow into a baby. If the egg is not fertilised by a sperm, the lining is shed and flows out of the body through the vagina. This flow is known as a woman’s period (menstruation).
The ovaries produce the hormones oestrogen and progesterone that cause ovulation and menstruation. Menopause occurs when the levels of these hormones decrease. A menopausal woman’s periods stop and she is not able to become pregnant. The uterus becomes smaller, and the endometrium becomes thinner and inactive.
The female reproductive system
Types of uterine cancer
Uterine cancer can be either endometrial cancer (around 95% of all uterine cancers) or the less common uterine sarcoma (around 4% of all uterine cancers).
Most cancers of the uterus begin in the lining of the uterus (endometrium) and are called endometrial cancers. There are two main types:
- Type 1 cancers (linked to an excess of oestrogen) − Usually called endometrioid cancer, Type 1 cancers are the most common types of endometrial cancer. Subtypes include adenocarcinoma, adenoacanthoma and secretory carcinoma. They are usually slow growing and less likely to spread. They typically require less intensive treatment.
- Type 2 cancers (not linked to oestrogen) − Type 2 cancers are much less common. They include uterine carcinosarcomas (also known as malignant mixed Müllerian tumours), serous carcinoma and clear cell carcinoma. They grow faster than type 1 cancers and are more likely to spread. Treatment usually involves more extensive surgery followed by radiation therapy and chemotherapy.
These soft tissue sarcomas develop in the muscle of the uterus (myometrium) or the connective tissue supporting the endometrium, which is called the stroma. There are three types:
- leiomyosarcoma and undifferentiated sarcoma − These types are rare and may be more likely to spread to other parts of the body.
- endometrial stromal sarcoma − Rare, low-grade, slow-growing tumour.
Who gets uterine cancer?
Each year, about 2500 Australian women are diagnosed with uterine cancer. The majority of these women are over 50. It is the fifth most common cancer diagnosed in Australian women and the most commonly diagnosed gynaecological cancer in Australia. One in 60 women is likely to be diagnosed with uterine cancer by the age of 75.
What causes uterine cancer?
The exact cause of cancer of the uterus is unknown, but some factors seem to increase a woman’s risk:
- being over 50
- being postmenopausal
- having endometrial hyperplasia, a benign condition in which the endometrium thickens because of too much oestrogen
- never having children or being infertile
- starting periods early (before age 12)
- reaching menopause late (after age 55)
- having high blood pressure (hypertension)
- having diabetes
- being overweight or obese
- a family history of ovarian, uterine, breast or bowel cancer
- having an inherited genetic condition such as Lynch syndrome or Cowden syndrome
- previous ovarian tumours or polycystic ovary syndrome
- taking oestrogen hormone replacement without progesterone
- previous pelvic radiation for cancer
- taking tamoxifen, an anti-oestrogen drug used to treat breast cancer (talk to your doctor about the risks and benefits if you are concerned).
Many women who have risk factors don’t develop cancer of the uterus, and some women who get cancer have no risk factors.
Visit Cancer Prevention to read about ways to reduce your risk of developing cancer.