Physicians and researchers are still trying to determine what causes cancer of the uterus. At present, it is not known what causes this disease and why some women are affected while others are not. What is known is that certain factors are more common in women who develop uterine cancer than in those who do not.

The following risk factors are associated with an increased risk of uterine cancer:

• Early menstruation. Women who began menstruating at age 12 or earlier have a greater number of menstrual periods than women who started menstruating when they were older than age 12. This increase in the number of menstrual periods means a woman would have had more exposure of the endometrium to estrogen, which can lead to a greater risk of uterine cancer. Likewise, experiencing a late menopause increases the endometrium's exposure to estrogen, and the risk of developing uterine cancer.
• Not having children. Women who have never given birth have an increased risk of developing uterine cancer. In pregnancy, progesterone levels increase and estrogen levels decrease, reducing the risk of developing cancer of the uterus.
• Taking estrogen therapy. Many women have used estrogen replacement therapy (ERT) to control the symptoms associated with menopause to prevent osteoporosis and to reduce the risk of heart disease and stroke. Although there may be some beneficial reasons for women to take ERT, women who use ERT have an increased risk for developing cancer of the uterus. Using a combination of estrogen and progesterone (HRT) instead of estrogen alone decreases the higher risk of developing uterine cancer associated with the use of estrogen alone.
• Obesity. Women who are overweight have a greater risk of developing cancer of the uterus than women of normal weight. Researchers believe too much estrogen may be the reason why overweight women are more susceptible to this disease. Women with excess fat produce larger amounts of estrogen.
• High-fat diet. Women who eat a diet high in animal fats have an increased risk of developing endometrial cancer as well as other types of cancer. There may be a connection between foods high in fat and obesity, which may explain the increased risk.
• Taking tamoxifen. Tamoxifen is a drug that may be prescribed to prevent or treat breast cancer. Tamoxifen may increase the risk of developing uterine cancer. Since the risk is relatively small, about one woman in 500, the benefits of taking the drug to prevent or treat breast cancer may far outweigh the risk of developing endometrial cancer. However, women taking tamoxifen should be closely monitored for signs or symptoms of cancer of the uterus, and women are also advised by their primary doctor or gynecologist to report any abnormal bleeding to their physicians.
• Having a disease of the ovaries. Women who have polycystic ovary syndrome have an increased risk of developing uterine cancer.
• Family history of cancer. Women with a family history of one type of colorectal cancer (heredity nonpolyposis colorectal cancer) have a greatly increased risk of developing cancer of the uterus.

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External Sources American Cancer Society. Endometrial Cancer Resource Center. American Cancer Society. What causes colon and rectal cancer? . Accessed February 10, 2009