Estimating Breast Cancer Risk: Facts on Risks and Recurrence

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: http://www.cancer.gov/bcrisktool.

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).

4. 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.

5. 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.

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6. 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.

7. Are there ways to decrease the chance of developing breast cancer?

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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, postmenopausal 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 postmenopausal 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 continues to be analyzed. (http://www.cancer.gov/newscenter/pressreleases/STARresultsQandA)

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8. 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.

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

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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.

Source: U.S. National Institutes of Health, National Cancer Institute, http://www.cancer.gov