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Estimating Breast Cancer Risk: Questions and Answers

1. Who develops breast cancer?

Breast cancer is the most frequently diagnosed non-skin cancer in American women. An estimated 213,000 American women will be diagnosed with breast cancer in 2006. The risk of breast cancer increases as women get older. Over the years, researchers have identified certain characteristics, usually called risk factors, which 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 develop breast cancer.

2. What is the Breast Cancer Risk Assessment Tool?

The Breast Cancer Risk Assessment Tool is a computer program that was developed by scientists at the National Cancer Institute and the National Surgical Adjuvant Breast and Bowel Project (NSABP) to assist health care providers in discussing breast cancer risk with their female patients. The tool allows a health professional to project a woman's individual estimate of breast cancer risk over a 5-year period of time and over her lifetime and compares the woman's risk calculation with the average risk for a woman of the same age. The Breast Cancer Risk Assessment Tool can be found at:

3. 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. Two breast tissue abnormalities -- ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS) -- are associated with increased risk for developing invasive breast cancer.

  • Age. The risk of developing breast cancer increases with age. The majority of breast cancer cases occur in women older than age 50.

  • Age at menarche (first menstrual period). Women who had their first menstrual period before age 12 have a slightly increased risk of breast cancer.

  • Age at first live birth. Risk depends on age at first live birth and family history of breast cancer, as shown in the following table of relative risks.
Relative Risk of Developing Breast Cancer*
Age at first live birth 0 Affected Relatives 1 Affected Relatives 2 Affected Relatives
20 or younger 1 2.6 6.8
20-24 1.2 2.7 5.8
25-29 or no child 1.5 2.8 4.9
30 or older 1.9 2.8 4.2

For women with 0 or 1 affected relative, risks increase with age at first live birth. For women with 2 or more first degree relatives, risks decrease with age at first live birth.

Adapted from Table 1, Gail MH, Brinton LA, Byar DP, Corle DK, Green SB, Shairer C, Mulvihill JJ: Projecting individualized probabilities of developing breast cancer for white females who are being examined annually. J Natl Cancer Inst 81(24):1879-86, 1989. [PubMed Abstract]

  • Breast cancer among first-degree relatives (sisters, mother, daughters). Having one or more first-degree blood relatives who have been diagnosed with breast cancer increases a woman's chances of developing the disease.

  • Breast biopsies. Women who have had breast biopsies have an increased risk of breast cancer, especially if the biopsy showed a change in breast tissue, known as atypical hyperplasia. These women are at increased risk because of whatever prompted the biopsies, not because of the biopsies themselves.

  • Race. White women have greater risk of developing breast cancer than Black women (although Black women diagnosed with breast cancer are more likely to die of the disease).


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