Cancer of the uterus is one of the most common cancers of the female reproductive system. Endometrial carcinoma, which is cancer of the inner lining of the uterus (endometrium), is the more frequently seen uterine cancer although there are other types like uterine sarcoma and carcinosarcoma which occasionally arises. Uterine cancer is a malignant tumor of the uterus and should not be confused with benign growths like uterine fibroids and uterine polyps.
Types of Uterine Cancer
Endometrial cancer is the most common type of uterine cancer and starts in the inner lining of the uterus known as the endometrium.
Endometrial carcinomas can be divided into various subtypes, of which adenocarcinomas are the most common. Adenocarcinomas are cancers of the cells that form glands in the endometrium. Most endometrial carcinomas are typical adenocarcinomas, also known as endometrioid.
Other less common, but often more aggressive, subtypes are :
- Squamous cell carcinoma
- Papillary serous carcinoma
- Clear-cell carcinoma
- Poorly differentiated carcinoma
Cancer that starts in the supporting connective tissue (stroma) and muscle cells of the uterus is known as uterine sarcoma. Only a small percentage of uterine cancers belong to this group.
Uterine Carcinosarcoma (CS)
Another rarer type of uterine cancer is known as uterine carcinosarcoma (CS). CS also starts in the endometrium but shows features of both carcinoma and sarcoma when examined under the microscope. It has been suggested that CS may be a form of poorly differentiated carcinoma.
Based on their prognosis (outlook) and underlying cause, endometrial carcinoma may be divided into 2 types
- Type 1 cancers are those that are caused by an excess of the female hormone estrogen. These are less aggressive than type 2 cancers and since spread to other tissues is usually slow, the outlook is often better than type 2 cancers. Grades 1 and 2 endometrioid cancers belong to this group. Type 1 endometrial cancer is the most common type, accounting for nearly 80% of cases.
- Type 2 cancers are not estrogen dependent, although the exact cause is not known. Serous carcinoma, clear-cell carcinoma, poorly differentiated carcinoma, and grade 3 endometrioid cancers fall under this group. These cancers are more aggressive and tend to spread more rapidly hence their prognosis is not as good as type 1 cancers.
Causes and Risk Factors of Uterine Cancer
The exact cause of uterine cancer is not known but some factors cause a genetic mutation to occur within the cells of the endometrium, changing normal cells into abnormal cells.
The factors that may contribute to the development of uterine cancer includes :
- Age. Uterine cancer is a disease that is more often seen in older women. Women between the ages of 50 and 70 seem to be more at risk. It rarely develops in women under the age of 40.
- Family history. Uterine cancer tends to run in some families.
- Persistently high estrogen levels seem to play a significant role. Many of the risk factors for uterine cancer affect estrogen levels. A change in the balance of the two hormones, estrogen and progesterone, with a shift towards more estrogen, may increase a woman’s chances of developing endometrial cancer.
- Menopause. Changes in hormone levels during menopause may be the reason that endometrial cancer is more common in postmenopausal women.
- Early menarche (onset of menstruation). More years of menstruation, typically when menarche occurs before the age of 12 years and late menopause, after the age of 50, may raise a woman’s risk of endometrial cancer.
- Hormone replacement therapy (HRT). Women who are only on estrogen, without the use of progesterone, seem to be at considerable risk. The unopposed action of estrogen on the endometrium for a prolonged period may lead to the development of uterine cancer.
- Oral contraceptives, especially when used for a long time, may lower and not increase the risk of endometrial cancer. This protective action may continue for over 10 years after stopping the pills.
- Pregnancy causes a shift in the balance of hormones towards more progesterone hence women who have been pregnant a number of times may be protected against uterine cancer.
- Nulliparous women are those women who have never been pregnant and the risk of uterine cancer seems to be higher, especially when associated with infertility.
- Tamoxifen. Women who are on or have recently been on the drug tamoxifen used in the treatment of breast cancer may increase the risk of uterine cancer. However, in most cases, the benefits of tamoxifen outweigh its risk.
- Obesity is a major risk for uterine cancer.
- Diabetes mellitus (sugar diabetes).
- High blood pressure.
- History of uterine polyps.
- Women with hereditary nonpolyposis colon cancer (HNPCC) have a high risk of endometrial cancer.
- Endometrial hyperplasia (overgrowth of the endometrium), brought about by persistently high estrogen levels. Simple hyperplasia is not precancerous but atypical hyperplasia has a higher chance of becoming cancerous.
- Estrogen-producing ovarian tumors.
- Polycystic ovarian syndrome (PCOS), where there is a higher estrogen level in comparison to the progesterone level.
- History of breast cancer or ovarian cancer increases risk of uterine cancer.
- Pelvic radiation given to treat some other cancer can cause damage to the DNA of cells, thus increasing risk of developing cancer.