Estimating Breast Cancer Risk
Key Points
- 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.
- 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: http://www.cancer.gov/bcrisktool.
- 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 |
# of affected relatives |
0 |
1 |
2 or more |
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).
- Why are some other risk factors left out
of the Tool?
Other risk factors for breast cancer have been identified or proposed but
are not included in the Breast Cancer Risk Assessment Tool for several reasons:
because evidence that these factors contribute to breast cancer risk is not
conclusive, because researchers cannot determine whether these factors add
useful information to factors already in the model, or because data on other
risk factors was not available in the research data used to develop the model.
Such risk factors include: age at menopause, use of birth control pills, high
body mass index, a high-fat diet, alcohol, radiation exposure, and environmental
pollutants. Recently published research indicates that breast tissue density,
measured from mammograms, can add useful information, but risk models with
breast tissue density measurement still need to be validated with additional
independent studies. Research also indicates that other risk factors, such
as use of hormone therapy, might improve the tool.
- Is the Breast Cancer Risk Assessment Tool
useful for all women?
The Breast Cancer Risk Assessment Tool was developed for women in the United
States population age 35 years or older. It should not be used for women with
a previous diagnosis of breast cancer, women exposed to breast radiation for
treatment of Hodgkin lymphoma, or women who reside in, or recently migrated
from, regions with low breast cancer risk, such as rural China or Japan. More
accurate methods to project risk may be available for women with certain rare
identified mutations, such as alterations in the breast cancer susceptibility
genes BRCA1 and BRCA2. The Breast Cancer Risk Assessment Tool was developed
and has been validated in populations consisting mainly of non-Hispanic white
women. More research is needed to validate or refine the model for other racial
and ethnic groups.
- What are some of the latest research findings
on breast cancer risk?
Two studies in the September 6, 2006, issue of the Journal of the National
Cancer Institute identified breast density as an important risk factor.*
In one, a study of 11,638 women diagnosed with breast cancer, researchers
identified different sets of risk factors in pre- and post-menopausal women.
For pre-menopausal women, the risk factors included age, breast density, family
history of breast cancer, and prior cancer diagnosis. For post-menopausal
women, the risk factors included ethnicity, body mass index, age at natural
menopause, use of hormone therapy, and a prior false-positive mammogram, in
addition to all the risk factors for pre-menopausal women. The two separate
models in this study for predicting breast cancer in pre- and post-menopausal
women may be particularly helpful in identifying women at high risk for breast
cancer.
The other study adds breast density and weight to the Gail model, a model
that is the basis for the Breast Cancer Risk Assessment Tool (see Question
2). As before, the new model can be used to project risk over 5, 10, 20
and 30 year intervals. The new model predicted higher risks than the previous
model in women with high breast density, and previous analyses indicated that
the new model had modestly higher accuracy. Independent validation studies
are needed before this model should be used for counseling, and before making
a permanent change to the Breast Cancer Risk Assessment Tool.
- Are there ways to decrease the chance of
developing breast cancer?
Launched in April 1992, the Breast Cancer Prevention Trial (BCPT) was designed
to see whether the drug tamoxifen could prevent breast cancer in women with
an increased risk. Data reported in 1998 showed that both pre- and post-menopausal
women taking tamoxifen had 49 percent fewer diagnosed cases of breast cancer.
These results were also the first clear indication that a chemopreventive
agent could be effective in preventing cancer in a high-risk population. For
women over 50, tamoxifen was associated with serious side effects, such as
endometrial cancer and blood clots. (http://www.cancer.gov/cancertopics/factsheet/Prevention/breast-cancer)
Starting in 1999, post-menopausal women ages 35 or older at increased risk
for breast cancer participated in the Study of Tamoxifen and Raloxifene (STAR).
The study compared tamoxifen with raloxifene, an osteoporosis drug. The initial
results of the trial were announced on April 17, 2006 (see http://www.cancer.gov/newscenter/pressreleases/STARresultsApr172006),
and showed that the drug raloxifene works as well as tamoxifen in reducing
breast cancer risk for post-menopausal women at increased risk of the disease.
In STAR, both drugs reduced the risk of developing invasive breast cancer
by about 50 percent. In addition, within the study, women who were prospectively
and randomly assigned to take raloxifene daily, and who were followed for
an average of about four years, had 36 percent fewer uterine cancers and 29
percent fewer blood clots than the women who were assigned to take tamoxifen.
Uterine cancers, especially endometrial cancers, are a rare but serious side
effect of tamoxifen. Both tamoxifen and raloxifene are known to increase a
woman’s risk of blood clots. Data from STAR continue to be analyzed.
(http://www.cancer.gov/cancertopics/factsheet/STARresultsQandA)
- How did BCPT and STAR use the Breast Cancer
Risk Assessment Tool to add to our knowledge of breast cancer risk?
Both breast cancer prevention studies, BCPT and STAR, explored ways of reducing
the risk of developing breast cancer; their findings have increased our knowledge
of risk. Both trials involved women who have not had breast cancer, but were
at high risk of developing it. BCPT used the Breast Cancer Risk Assessment
Tool to determine eligible participants by projecting each woman's individualized
estimate of breast cancer risk. The projections were accurate; thus the BCPT
results validated the Breast Cancer Risk Assessment Tool. STAR researchers
used the Breast Cancer Risk Assessment Tool for determining eligibility for
enrollment. All STAR participants had to have an increased risk of breast
cancer equivalent to or greater than that of an average 60- to 64-year-old
woman.
- What else can a woman do about breast cancer?
NCI recommends that women in their 40s and older get screening mammograms
every one to two years. Women who are at higher than average risk of breast
cancer should talk with their health care providers about whether to have
mammograms before age 40 and how often to have them. Women also can take an
active part in the early detection of breast cancer by having regular clinical
breast exams (breast exams performed by health professionals).
Advances in screening have provided new tools for detection. In September
of 2005, preliminary results from a large clinical trial of digital vs. film
mammography found no difference in detecting breast cancer for the general
populations of women in the trial. However, the Digital Mammographic Imaging
Screening Trial (DMIST) found that women with dense breasts, who are pre-
or perimenopausal (women who had a last menstrual period within 12 months
of their mammograms), or who are younger than age 50, may benefit from having
a digital rather than a regular film mammogram. More information about DMIST
can be found at http://www.cancer.gov/newscenter/pressreleases/DMISTQandA.
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* Barlow WE, White E, Ballard-Barbash R, Vacek P, Titus-Ernstoff L, Carney
PA, Tice JA, Buist, DSM, Geller BM, Rosenberg R, Yankaskas BC, Kerlikowske K.
Prospective Breast Cancer Risk Prediction Model for Women Undergoing Screening
Mammography. Journal of the National Cancer Institute September 6,
2006; 17:Vol. 98.
Chen J, Pee D, Ayyagari R, Graubard B, Schairer C, Byrne C, Benichou J, Gail,
MH. Projecting Absolute Invasive Breast Cancer Risk in White Women With Model
That Includes Mammographic Density. Journal of the National Cancer Institute
September 6, 2006; 17:Vol. 98.
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