NIH Press Release
NATIONAL INSTITUTES OF HEALTH
National Cancer Institute

FOR IMMEDIATE RELEASE
Wednesday, September 30, 1998

NCI Press Office
(301) 496-6641


Estimating Breast Cancer Risk

The Breast Cancer Risk Assessment Tool is a computer program that women and their health care providers can use to estimate a woman's chances of developing breast cancer based on several recognized risk factors. The Breast Cancer Risk Assessment Tool also provides information on the drug tamoxifen. Scientists at the National Cancer Institute and the National Surgical Adjuvant Breast and Bowel Project developed this tool.

This fact sheet provides information on the Breast Cancer Risk Assessment Tool and about breast cancer risk and the drug tamoxifen. A recent study, the Breast Cancer Prevention Trial, has shown that tamoxifen can reduce the likelihood of developing breast cancer in women at increased risk for the disease.

1. Who gets breast cancer?

Breast cancer is the most frequently diagnosed non-skin cancer in American women. The risk of breast cancer increases as women get older. No one knows why some women develop breast cancer and others do not. Over the years, researchers have identified certain characteristics, usually called "risk factors," that influence a woman's chance of getting the disease. Still, many women who develop breast cancer have no known risk factors other than growing older, and many women with known risk factors do not get breast cancer.

2. What are the risk factors used to estimate breast cancer risk in the Breast Cancer Risk Assessment Tool?

The risk factors included in the tool are: personal history of breast abnormalities, current age, age at first menstrual period, age at first live birth, breast cancer history of close relatives, whether a woman has had a breast biopsy, and race.

3. Why are some other risk factors left out?

Other risk factors for breast cancer have been identified or proposed, but are not included in the Breast Cancer Risk Assessment Tool for two reasons: either evidence that these factors contribute to breast cancer risk is not conclusive, or researchers cannot determine how much these factors contribute to breast cancer risk as precisely as with the factors listed above. Such risk factors include: age at menopause, dense breast tissue, use of birth control pills or hormone replacement therapy, a high-fat diet, alcohol, radiation exposure, and environmental pollutants.

4. What does the Breast Cancer Risk Assessment Tool do?

The Breast Cancer Risk Assessment Tool estimates a woman's risk of developing breast cancer for two time periods: over the next five years and for her lifetime. The tool compares these risks (given as a percentage) to those of a woman of the same age with NO risk factors other than her age, and with the risk of women who were eligible to participate in the Breast Cancer Prevention Trial.

5. What is the Breast Cancer Prevention Trial (BCPT)?

The BCPT is a clinical trial in which 13,388 women at increased risk of developing breast cancer were randomly assigned to take either the drug tamoxifen or a placebo (an inactive pill that looked like tamoxifen) to see if tamoxifen could prevent breast cancer.

6. Did the Breast Cancer Prevention Trial show that tamoxifen can prevent breast cancer?

In the BCPT, breast cancer was diagnosed half as often in the women who were assigned to take tamoxifen compared with women who were assigned to take the placebo. Tamoxifen offered this benefit along with no apparent increased risk of serious side effects for women ages 35 to 49, but the prevention benefit for women ages 50 and older came with an increased risk of serious side effects.

7. What is tamoxifen?

Tamoxifen is a pill that has been used for more than 20 years to treat patients with breast cancer. This drug works against breast cancer, in part, by interfering with the activity of estrogen, a female hormone that promotes the growth of breast cancer cells. For this reason, tamoxifen is often called an "anti-estrogen."

8. What are the adverse effects of tamoxifen?

In the BCPT, tamoxifen caused mild, non-life-threatening side effects in some women. These mild side effects included hot flashes and vaginal discharge.

In addition, women over age 50 who took tamoxifen had an increased chance of developing three rare but serious health problems: endometrial cancer (cancer of the lining of the uterus), pulmonary embolism (a blood clot in the lung), and deep vein thrombosis (blood clots in major veins).

9. How great is the risk of endometrial cancer for women who take tamoxifen?

In the BCPT, tamoxifen more than doubled a woman's chances of developing endometrial cancer compared with women of the same age who did not take tamoxifen. The risk of endometrial cancer from tamoxifen was similar to that for postmenopausal women who take estrogen replacement therapy.

The increased risk for endometrial cancer was seen mainly in women ages 50 and older who were taking tamoxifen: they had four times the chances of developing endometrial cancer as women of the same age who were not taking tamoxifen. The risk of developing endometrial cancer in women ages 50 and older on the BCPT was equivalent to 30 cases of endometrial cancer per 10,000 women per year in the women assigned to take tamoxifen compared to 8 cases per 10,000 women per year in the women assigned to take placebo.

Women taking tamoxifen should be closely monitored by their health care provider for possible signs or symptoms of endometrial cancer, especially abnormal vaginal bleeding. Women who have had a hysterectomy have no known risk of developing endometrial cancer.

10. How great is the risk of serious blood clots (deep vein thrombosis and pulmonary embolism) for women who take tamoxifen?

Deep vein thrombosis occurs when blood clots form in a major vein. Sometimes the clot can break off and travel to the lung, becoming a pulmonary embolism. In the BCPT, tamoxifen nearly tripled a woman's chances of developing a deep vein thrombosis or pulmonary embolism. This increased risk due to tamoxifen is about the same as that for a woman taking birth control pills or estrogen replacement therapy.

11. Should all women at increased risk of breast cancer take tamoxifen?

Tamoxifen may not be right for every woman. Women should discuss with their health care provider their individual risks and the potential benefits of taking tamoxifen. However, women at increased risk for blood clots and those who are pregnant or who plan to become pregnant should not take tamoxifen. Animal studies have suggested that the use of tamoxifen during pregnancy might harm the fetus. Women taking any birth control pills or hormone replacements must stop those medications before beginning tamoxifen. Premenopausal women who take tamoxifen should use some method of birth control other than birth control pills.

12. Are there other ways to prevent breast cancer?

Tamoxifen is the only proven way to reduce the risk of breast cancer. Studies of other ways to prevent breast cancer are under way and planned. Postmenopausal women ages 35 or older at increased risk for breast cancer are encouraged to consider participating in the Study of Tamoxifen and Raloxifene (STAR). The study will compare tamoxifen with raloxifene, an osteoporosis drug which may also have breast cancer prevention effects. STAR will enroll 22,000 high-risk women and is scheduled to begin at centers across the United States and in Canada in early 1999.

Women who wish to be put on a mailing list to receive information about STAR can do so by Internet (http://www.nsabp.pitt.edu), by mail (National Surgical Adjuvant Breast and Bowel Project, Box 21, Pittsburgh, Pa. 15261), or by fax (412-330-4660). Once the trial has begun, women can get information from the NCI's Cancer Information Service at 1-800-4-CANCER.

13. Is the Breast Cancer Risk Assessment Tool useful for all women?

The Breast Cancer Risk Assessment Tool gives an estimated risk. It is not accurate for women who are younger than age 20, who have already had a diagnosis of breast cancer or who are known to have specific alterations in breast cancer susceptibility genes (BRCA1 or BRCA2). There is also some doubt about whether women from other countries will have accurate results because the tool is based on U.S. women.

14. What else can a woman do about breast cancer?

Women can take an active part in the early detection of breast cancer by having regular screening mammograms and clinical breast exams (breast exams performed by health professionals). Many women also perform breast self-exams, although this is not a substitute for clinical breast exams or mammography.

Information Resources from the National Cancer Institute

For more information or to receive the publications listed below, call the National Cancer Institute's Cancer Information Service at 1-800-4-CANCER. For easy access to clinical trials information from NCI, go to http://cancerTrials.nci.nih.gov on the World Wide Web.

Fact Sheets Questions and Answers About the Breast Cancer Prevention Trial Clinical Trials: Get the Facts About Cancer Prevention Studies Questions and Answers About Tamoxifen Preguntas y Respuestas Acerca del Tamoxifen

Booklets Understanding Breast Changes: A Health Guide for All Women What You Need To Know About Breast Cancer