Breast Cancer Risk in American Women
Breast Cancer Risk in American Women
Key Points
- Based on current breast cancer incidence rates, experts
estimate that about one out of every eight women born today will be
diagnosed with breast cancer at some time during her life.
- The strongest risk factor for breast cancer is age. A woman’s risk of developing this disease increases as she gets older.
- Other factors can also increase a woman’s risk of developing
breast cancer, including inherited changes in certain genes, a personal
or family history of breast cancer, having dense breasts, beginning to
menstruate before age 12, starting menopause after age 55, having a
first full-term pregnancy after age 30, never having been pregnant,
obesity after menopause, and alcohol use.
What is the average American woman’s risk of developing breast cancer during her lifetime?
Based on current incidence rates, 12.4 percent of women born in the United States today will develop breast cancer at some time during their lives (1). This estimate, from the most recent SEER Cancer Statistics Review
(a report published annually by the National Cancer Institute’s [NCI]
Surveillance, Epidemiology, and End Results [SEER] Program), is based on
breast cancer statistics for the years 2007 through 2009.
This
estimate means that, if the current incidence rate stays the same, a
woman born today has about a 1 in 8 chance of being diagnosed with
breast cancer at some time during her life. On the other hand, the
chance that she will never have breast cancer is 87.6 percent, or about 7
in 8.
In the 1970s, the lifetime risk of being diagnosed with breast cancer in the United States was just under 10 percent (or about 1 in 10).
The
last five annual SEER reports show the following estimates of lifetime
risk of breast cancer, all very close to a lifetime risk of 1 in 8:
- 12.7 percent for 2001 through 2003
- 12.3 percent for 2002 through 2004
- 12.0 percent for 2003 through 2005
- 12.1 percent for 2004 through 2006
- 12.4 percent for 2005 through 2007
SEER
statisticians expect some variability from year to year. Slight
changes, such as the ones observed over the last 5 years, may be
explained by a variety of factors, including minor changes in risk
factor levels in the population, slight changes in breast cancer
screening rates, or just random variability inherent in the data.
What is the average American woman’s risk of being diagnosed with breast cancer at different ages?
Many
women are more interested in the risk of being diagnosed with breast
cancer at specific ages or over specific time periods than in the risk
of being diagnosed at some point during their lifetime. Estimates by
decade of life are also less affected by changes in incidence and mortality rates than longer-term estimates. The SEER report estimates the risk of developing breast cancer in 10-year age intervals (1).
According to the current report, the risk that a woman will be
diagnosed with breast cancer during the next 10 years, starting at the
following ages, is as follows:
- Age 30 . . . . . . 0.44 percent (or 1 in 227)
- Age 40 . . . . . . 1.47 percent (or 1 in 68)
- Age 50 . . . . . . 2.38 percent (or 1 in 42)
- Age 60 . . . . . . 3.56 percent (or 1 in 28)
- Age 70 . . . . . . 3.82 percent (or 1 in 26)
These
probabilities are averages for the whole population. An individual
woman’s breast cancer risk may be higher or lower depending on a number
of known factors (see Question 3) and on factors that are not yet fully
understood. To calculate an individual woman’s estimated risk, health
professionals can use the Breast Cancer Risk Assessment Tool.
For more information about risk of breast cancer at specific ages and for specific time periods, see Table 4.18 in the SEER report.
What factors increase a woman’s risk of breast cancer?
The strongest risk factor
for breast cancer is age. A woman’s risk of developing this disease
increases as she gets older. The risk of breast cancer, however, is not
the same for all women in a given age group. Research has shown that
women with the following risk factors have an increased chance of
developing breast cancer.
- Genetic alterations (changes): Inherited changes in certain genes (including BRCA1, BRCA2,
and others) increase the risk of breast cancer. These changes are
estimated to account for no more than about 10 percent of all breast
cancers. However, women who carry changes in these genes have a much
higher risk of breast cancer than women who do not carry these changes.
- Mammographic breast density: The glandular (milk-producing) and connective tissue of the breast are mammographically dense—that is, they appear white on a mammogram.
In contrast, fatty tissue of the breast is not mammographically dense
and appears dark. Women who have a high percentage of breast tissue that
appears dense on a mammogram have a higher risk of breast cancer than
women of similar age who have little or no dense breast tissue. In
general, younger women have denser breasts than older women. As a woman
ages, the amount of glandular tissue normally decreases and the amount
of fatty tissue increases. Abnormalities, such as tumors, in dense
breasts can be more difficult to detect on a mammogram because tumors
often also appear white.
- Family history:
A woman’s chance of developing breast cancer increases if her mother,
sister, and/or daughter have been diagnosed with the disease, especially
if they were diagnosed before age 50. Having a close male blood
relative with breast cancer also increases a woman's risk of developing
the disease.
- Personal history of breast cancer: Women who have had breast cancer are more likely to develop a second breast cancer.
- Certain breast changes found on biopsy:
Looking at breast tissue under a microscope allows doctors to determine
whether a suspicious finding (one detected by a mammogram, for example)
represents cancer or another type of breast change. Most breast changes
turn out not to be cancer, but some may increase the risk of developing
breast cancer. Changes that are associated with an increased risk of
breast cancer include atypical hyperplasia (a noncancerous condition in which cells have abnormal features and are increased in number), lobular carcinoma in situ (LCIS) (abnormal cells are found in the lobules of the breast), and ductal carcinoma in situ
(DCIS; abnormal cells are found in the lining of breast ducts). Because
some cases of DCIS will eventually become cancer, this type of breast
change is actively treated. Women with atypical hyperplasia or LCIS are
usually monitored carefully and not actively treated. In addition, women
who have had two or more breast biopsies for other noncancerous
conditions also have an increased risk of developing breast cancer. This
increased risk is due to the conditions that led to the biopsies and
not to the biopsy procedures themselves.
- Radiation therapy:
Women who had radiation therapy to the chest (including the breasts)
before age 30 have an increased risk of developing breast cancer
throughout their lives. This includes women treated for Hodgkin
lymphoma. Studies show that the younger a woman was when she received
treatment, the higher her risk of developing breast cancer later in
life.
- Alcohol: Studies indicate that the more alcohol a woman drinks, the greater her risk of breast cancer.
- Reproductive and menstrual history: Women who had their first menstrual period before age 12 or who went through menopause
after age 55 have an increased risk of developing breast cancer. Women
who had their first full-term pregnancy after age 30 or who have never
had a full-term pregnancy are also at increased risk of breast cancer.
- Long-term use of menopausal hormone therapy:
Women who used combined estrogen and progestin menopausal hormone
therapy for more than 5 years have an increased chance of developing
breast cancer.
- DES (diethylstilbestrol):
The drug DES was given to some pregnant women in the United States
between 1940 and 1971 to prevent miscarriage. Women who took DES during
pregnancy have a slightly increased risk of breast cancer. Women who
were exposed to DES in utero—that is, whose mothers took DES while they
were pregnant—may have a slightly increased risk of breast cancer after
age 40.
- Body weight: Studies have found that among postmenopausal
women who have not used menopausal hormone therapy, the chance of
getting breast cancer is higher in women who are overweight or obese
than in women of a healthy weight.
- Physical activity level: Women who are physically inactive throughout life may have an increased risk of breast cancer.
- Race:
In the United States, breast cancer is diagnosed more often in white
women than in African American/black, Hispanic/Latina, Asian/Pacific
Islander, or American Indian/Alaska Native women.
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