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The key to finding breast cancer is early detection, and the key to early
detection is screening: looking for cancer in women who have no symptoms
of disease. The best available tool is a regular screening
mammogram--x-ray
of the breast--coupled with a clinical
breast exam--by a doctor or nurse.
Mammography
A mammogram is
an x-ray of the breast. Cancers that are found
on mammograms but that cannot be felt (nonpalpable
cancers) usually are smaller than cancers that can be felt, and
they are less likely to have spread.
Mammography is not foolproof.
Some breast changes, including lumps that can be felt, do not show up
on a mammogram. Changes can be especially difficult to spot in the dense,
glandular breasts of younger women. This is why women of all ages should
have their breasts examined every year by a physician or trained health
professional.
~ A lump should never
be ignored just
because it is not visible on a mammogram.~
Two Kinds of
Mammography: Diagnostic and Screening
If a woman visits her doctor because of unusual breast changes such as
a lump, pain, nipple thickening or discharge, or changes in breast size
or shape, or has a suspicious screening mammogram, the doctor often asks
her to have a diagnostic mammogram:
an x-ray of the breast to help assess her symptoms. A diagnostic mammogram
is a basic medical tool, and it is appropriate for women of any age.
This booklet discusses screening mammograms: x-rays that are used to
look for breast changes in women who have no signs of breast cancer.
(Even though the woman has no symptoms of breast disease, a diagnosis of
breast cancer can begin with a doctor checking a screening mammogram.)
What Are the Benefits
of Screening Mammography?
High-quality mammography is the most effective tool now available to
detect breast cancer early, before symptoms appear--often before a
breast lump can even be felt. Regularly scheduled mammograms can
decrease a woman's chance of dying from breast cancer. For some women,
early detection may prevent the need to remove the entire breast or
receive chemotherapy.
Who Benefits From
Screening Mammography?
Studies done over the past 30 years clearly show that regular screening
mammography significantly reduces the death rate from breast cancer in
women over the age of 50. Recent results from studies show that regular
mammography also reduces death rates from breast cancer in women who
begin screening in their forties.
The effectiveness of mammography seems to increase as a woman ages,
and the time it takes for benefits to emerge appears to take longer in
younger women.
Who Is at Average
Risk for Breast Cancer?
Simply being a woman and getting older puts you at average risk
for developing breast cancer. The older you are, the greater your chance
of getting breast cancer. No woman should consider herself too old to
need regular screening mammograms.
Who Is at Higher Than
Average Risk for Breast Cancer?
One or more of the following conditions place a woman at higher than
average risk for breast cancer:
- personal history of a prior breast cancer
- evidence of a specific genetic change that increases
susceptibility to breast cancer (See Gene Testing for Breast Cancer
Susceptibility, page 18.)
- mother, sister, daughter, or two or more close relatives, such as
cousins, with a history of breast cancer (especially if diagnosed at
a young age)
- a diagnosis of a breast condition that may predispose a woman to breast
cancer (i.e., atypical hyperplasia),
or a history of two or more breast biopsies for benign breast disease
(See Benign Breast Conditions and the Risk for Breast Cancer, page 26.)
 Also
playing a role in a heightened risk for breast cancer is breast
density. Women ages 45 or older who have at least 75 percent dense
tissue on a mammogram are at elevated risk. And a slight increase in the
risk of breast cancer is associated with having a first birth at age 30
or older.
In addition, women who receive chest irradiation for conditions such
as Hodgkin's disease at age 30 or younger remain at higher risk for
breast cancer throughout their lives. These women require meticulous
surveillance for breast cancer.
These factors that increase cancer risk--risk
factors--do not by themselves cause cancer. Having one or more
does not mean that you are certain or even likely to develop breast cancer.
Even among women with no other risk factors except a strong family history--for
example, both a mother and a sister or two sisters with early onset breast
cancer--three-fourths will not develop the disease.
Clearly, there is much yet to be learned about what causes breast
cancer.
~ On the other hand,
not having any of the known risk factors
does not mean that you are "safe." Most women who develop
breast cancer do not have a strong family history of breast
cancer or fall into any special higher risk category. ~
What Are the
Limitations of Screening Mammography?
Early detection by mammography does not guarantee that a woman's life
will be saved. It may not help a woman who has a fast-growing cancer
that has spread to other parts of her body before being detected. Also,
about half of the women whose breast cancers are detected by mammography
would not have died from cancer, even if they had waited until the lump
could be felt, because their tumors are slow-growing and treatable.
False Negative Mammograms
Breasts of younger women contain many glands and ligaments. Because their
breasts appear dense on mammograms, it is difficult to see tumors or to
distinguish between normal and abnormal breast conditions. As a woman
grows older, the glandular and fibrous tissues of her breasts gradually
give way to less dense fatty tissues. Mammograms can then see into the
breast tissue more easily to detect abnormal changes. About 25 percent
of breast tumors are missed in women in their forties, compared to about
10 percent of women older than age 50. These are called false
negatives. A normal mammogram in a woman with symptoms does not
rule out breast cancer. Sometimes a clinical breast exam by a doctor or
nurse can reveal a breast lump that is missed by a mammogram.
False Positive Mammograms
Between 5 and 10 percent of mammogram results are abnormal and require
more testing (more mammograms, fine needle aspiration,
ultrasound, or biopsy),
and most of the followup tests confirm that no cancer was present. It
is estimated that a woman who has yearly mammograms between ages 40 and
49 would have about a 30 percent chance of having a false
positive mammogram at some point in that decade, and about a 7
to 8 percent chance of having a breast biopsy within the 10-year period.
The estimate for false positive mammograms is about 25 percent for women
ages 50 or older.
Increased Cases of Ductal Carcinoma In Situ (DCIS)
The increased use of screening mammography has increased the detection
of small abnormal tissue growths confined to the milk ducts in the breast,
called ductal carcinoma in situ
(DCIS). Doctors don't know which, if any, cases of DCIS may become
life threatening. Usually, the growth is removed surgically, and radiation
treatment is often given.
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