What is breast cancer?
Breast cancer is a malignant tumor that starts in the cells of the breast. A malignant tumor
is a group of cancer cells that can grow into (invade) surrounding tissues or spread
(metastasize) to distant areas of the body. The disease occurs almost entirely in women,
but men can get it, too.
Breast cancer is a malignant tumor that starts in the cells of the breast. A malignant tumor
is a group of cancer cells that can grow into (invade) surrounding tissues or spread
(metastasize) to distant areas of the body. The disease occurs almost entirely in women,
but men can get it, too.
The normal breast
To understand breast cancer, it helps to have some basic knowledge about the normal
structure of the breasts, shown in the diagram below.
The female breast is made up mainly of lobules (milk-producing glands), ducts (tiny
tubes that carry the milk from the lobules to the nipple), and stroma (fatty tissue and
connective tissue surrounding the ducts and lobules, blood vessels, and lymphatic
vessels).
To understand breast cancer, it helps to have some basic knowledge about the normal
structure of the breasts, shown in the diagram below.
The female breast is made up mainly of lobules (milk-producing glands), ducts (tiny
tubes that carry the milk from the lobules to the nipple), and stroma (fatty tissue and
connective tissue surrounding the ducts and lobules, blood vessels, and lymphatic
vessels).
Most breast cancers begin in the cells that line the ducts (ductal cancers). Some begin in
the cells that line the lobules (lobular cancers), while a small number start in other
tissues.
the cells that line the lobules (lobular cancers), while a small number start in other
tissues.
The lymph (lymphatic) system of the breast
The lymph system is important to understand because it is one way breast cancers can
spread. This system has several parts.
Lymph nodes are small, bean-shaped collections of immune system cells (cells that are
important in fighting infections) that are connected by lymphatic vessels. Lymphatic
vessels are like small veins, except that they carry a clear fluid called lymph (instead of
blood) away from the breast. Lymph contains tissue fluid and waste products, as well as
immune system cells. Breast cancer cells can enter lymphatic vessels and begin to grow
in lymph nodes.
The lymph system is important to understand because it is one way breast cancers can
spread. This system has several parts.
Lymph nodes are small, bean-shaped collections of immune system cells (cells that are
important in fighting infections) that are connected by lymphatic vessels. Lymphatic
vessels are like small veins, except that they carry a clear fluid called lymph (instead of
blood) away from the breast. Lymph contains tissue fluid and waste products, as well as
immune system cells. Breast cancer cells can enter lymphatic vessels and begin to grow
in lymph nodes.
Most lymphatic vessels in the breast connect to lymph nodes under the arm (axillary
nodes). Some lymphatic vessels connect to lymph nodes inside the chest (internal
mammary nodes) and either above or below the collarbone (supraclavicular or
infraclavicular nodes).
nodes). Some lymphatic vessels connect to lymph nodes inside the chest (internal
mammary nodes) and either above or below the collarbone (supraclavicular or
infraclavicular nodes).
If the cancer cells have spread to lymph nodes, there is a higher chance that the cells
could have also gotten into the bloodstream and spread (metastasized) to other sites in the
body. The more lymph nodes with breast cancer cells, the more likely it is that the cancer
may be found in other organs as well. Because of this, finding cancer in one or more
lymph nodes often affects the treatment plan. Still, not all women with cancer cells in
their lymph nodes develop metastases, and some women can have no cancer cells in their
lymph nodes and later develop metastases.
could have also gotten into the bloodstream and spread (metastasized) to other sites in the
body. The more lymph nodes with breast cancer cells, the more likely it is that the cancer
may be found in other organs as well. Because of this, finding cancer in one or more
lymph nodes often affects the treatment plan. Still, not all women with cancer cells in
their lymph nodes develop metastases, and some women can have no cancer cells in their
lymph nodes and later develop metastases.
Types of breast cancers
Breast cancer can be separated into different types based on the way the cancer cells look
under the microscope.
Most breast cancers are carcinomas, a type of cancer that starts in the cells (epithelial
cells) that line organs and tissues like the breast. In fact, breast cancers are often a type of
carcinoma called adenocarcinoma, which is carcinoma that starts in glandular tissue.
Other types of cancers can occur in the breast, too, such as sarcomas, which start in the
cells of muscle, fat, or connective tissue.
In some cases a single breast tumor can be a combination of different types or be a
mixture of invasive and in situ cancer. And in some rarer types of breast cancer, the
cancer cells may not form a tumor at all.
Breast cancer can also be classified based on proteins on or in the cancer cells, into
groups like hormone receptor-positive or triple-negative. These are discussed in the
section “How is breast cancer classified?”
Breast cancer can be separated into different types based on the way the cancer cells look
under the microscope.
Most breast cancers are carcinomas, a type of cancer that starts in the cells (epithelial
cells) that line organs and tissues like the breast. In fact, breast cancers are often a type of
carcinoma called adenocarcinoma, which is carcinoma that starts in glandular tissue.
Other types of cancers can occur in the breast, too, such as sarcomas, which start in the
cells of muscle, fat, or connective tissue.
In some cases a single breast tumor can be a combination of different types or be a
mixture of invasive and in situ cancer. And in some rarer types of breast cancer, the
cancer cells may not form a tumor at all.
Breast cancer can also be classified based on proteins on or in the cancer cells, into
groups like hormone receptor-positive or triple-negative. These are discussed in the
section “How is breast cancer classified?”
Ductal carcinoma in situ
Ductal carcinoma in situ (DCIS; also known as intraductal carcinoma) is considered noninvasive
or pre-invasive breast cancer. DCIS means that cells that lined the ducts have
changed to look like cancer cells. The difference between DCIS and invasive cancer is
that the cells have not spread (invaded) through the walls of the ducts into the
surrounding breast tissue. Because it hasn’t invaded, DCIS can’t spread (metastasize)
outside the breast. DCIS is considered a pre-cancer because some cases can go on to
become invasive cancers. Right now, though, there is no good way to know for certain
which cases will go on to become invasive cancers and which ones won’t.
Ductal carcinoma in situ (DCIS; also known as intraductal carcinoma) is considered noninvasive
or pre-invasive breast cancer. DCIS means that cells that lined the ducts have
changed to look like cancer cells. The difference between DCIS and invasive cancer is
that the cells have not spread (invaded) through the walls of the ducts into the
surrounding breast tissue. Because it hasn’t invaded, DCIS can’t spread (metastasize)
outside the breast. DCIS is considered a pre-cancer because some cases can go on to
become invasive cancers. Right now, though, there is no good way to know for certain
which cases will go on to become invasive cancers and which ones won’t.
About 1 in 5 new breast cancer cases will be DCIS. Nearly all women diagnosed at this
early stage of breast cancer can be cured.
early stage of breast cancer can be cured.
Invasive (or infiltrating) ductal carcinoma
This is the most common type of breast cancer. Invasive (or infiltrating) ductal carcinoma
(IDC) starts in a milk duct of the breast, breaks through the wall of the duct, and grows
into the fatty tissue of the breast. At this point, it may be able to spread (metastasize) to
other parts of the body through the lymphatic system and bloodstream. About 8 of 10
invasive breast cancers are infiltrating ductal carcinomas.
This is the most common type of breast cancer. Invasive (or infiltrating) ductal carcinoma
(IDC) starts in a milk duct of the breast, breaks through the wall of the duct, and grows
into the fatty tissue of the breast. At this point, it may be able to spread (metastasize) to
other parts of the body through the lymphatic system and bloodstream. About 8 of 10
invasive breast cancers are infiltrating ductal carcinomas.
Invasive (or infiltrating) lobular carcinoma
Invasive lobular carcinoma (ILC) starts in the milk-producing glands (lobules). Like IDC,
it can spread (metastasize) to other parts of the body. About 1 in 10 invasive breast
cancers is an ILC. Invasive lobular carcinoma may be harder to detect by a mammogram
than invasive ductal carcinoma.
Invasive lobular carcinoma (ILC) starts in the milk-producing glands (lobules). Like IDC,
it can spread (metastasize) to other parts of the body. About 1 in 10 invasive breast
cancers is an ILC. Invasive lobular carcinoma may be harder to detect by a mammogram
than invasive ductal carcinoma.
Less common types of breast cancer
Inflammatory breast cancer
This uncommon type of invasive breast cancer accounts for about 1% to 3% of all breast
cancers. Usually there is no single lump or tumor. Instead, inflammatory breast cancer
(IBC) makes the skin on the breast look red and feel warm. It also may give the breast
skin a thick, pitted appearance that looks a lot like an orange peel. Doctors now know that
these changes are not caused by inflammation or infection, but by cancer cells blocking
lymph vessels in the skin. The affected breast may become larger or firmer, tender, or
itchy.
Inflammatory breast cancer
This uncommon type of invasive breast cancer accounts for about 1% to 3% of all breast
cancers. Usually there is no single lump or tumor. Instead, inflammatory breast cancer
(IBC) makes the skin on the breast look red and feel warm. It also may give the breast
skin a thick, pitted appearance that looks a lot like an orange peel. Doctors now know that
these changes are not caused by inflammation or infection, but by cancer cells blocking
lymph vessels in the skin. The affected breast may become larger or firmer, tender, or
itchy.
In its early stages, inflammatory breast cancer is often mistaken for an infection in the
breast (called mastitis) and treated as an infection with antibiotics. If the symptoms are
caused by cancer, they will not improve, and a biopsy will find cancer cells. Because
there is no actual lump, it might not show up on a mammogram, which can make it even
harder to find it early. This type of breast cancer tends to have a higher chance of
spreading and a worse outlook (prognosis) than typical invasive ductal or lobular cancer.
For more details about this condition, see our document Inflammatory Breast Cancer.
breast (called mastitis) and treated as an infection with antibiotics. If the symptoms are
caused by cancer, they will not improve, and a biopsy will find cancer cells. Because
there is no actual lump, it might not show up on a mammogram, which can make it even
harder to find it early. This type of breast cancer tends to have a higher chance of
spreading and a worse outlook (prognosis) than typical invasive ductal or lobular cancer.
For more details about this condition, see our document Inflammatory Breast Cancer.
Paget disease of the nipple
This type of breast cancer starts in the breast ducts and spreads to the skin of the nipple
and then to the areola, the dark circle around the nipple. It is rare, accounting for only
about 1% of all cases of breast cancer. The skin of the nipple and areola often appears
crusted, scaly, and red, with areas of bleeding or oozing. The woman may notice burning
or itching.
Paget disease is almost always associated with either ductal carcinoma in situ (DCIS) or
infiltrating ductal carcinoma. Treatment often requires mastectomy. If no lump can be felt
in the breast tissue, and the biopsy shows DCIS but no invasive cancer, the outlook
(prognosis) is excellent. If invasive cancer is present, the prognosis is not as good, and
the cancer will need to be staged and treated like any other invasive cancer.
This type of breast cancer starts in the breast ducts and spreads to the skin of the nipple
and then to the areola, the dark circle around the nipple. It is rare, accounting for only
about 1% of all cases of breast cancer. The skin of the nipple and areola often appears
crusted, scaly, and red, with areas of bleeding or oozing. The woman may notice burning
or itching.
Paget disease is almost always associated with either ductal carcinoma in situ (DCIS) or
infiltrating ductal carcinoma. Treatment often requires mastectomy. If no lump can be felt
in the breast tissue, and the biopsy shows DCIS but no invasive cancer, the outlook
(prognosis) is excellent. If invasive cancer is present, the prognosis is not as good, and
the cancer will need to be staged and treated like any other invasive cancer.
Phyllodes tumor
This very rare breast tumor develops in the stroma (connective tissue) of the breast, in
contrast to carcinomas, which develop in the ducts or lobules. Other names for these
tumors include phylloides tumor and cystosarcoma phyllodes. These tumors are usually
benign but on rare occasions may be malignant.
Benign phyllodes tumors are treated by removing the tumor along with a margin of
normal breast tissue. A malignant phyllodes tumor is treated by removing it along with a
wider margin of normal tissue, or by mastectomy. Surgery is often all that is needed, but
these cancers might not respond as well to the other treatments used for more common
breast cancers. When a malignant phyllodes tumor has spread, it can be treated with the
chemotherapy given for soft-tissue sarcomas. See our document Sarcoma - Adult Soft
Tissue Cancer.
This very rare breast tumor develops in the stroma (connective tissue) of the breast, in
contrast to carcinomas, which develop in the ducts or lobules. Other names for these
tumors include phylloides tumor and cystosarcoma phyllodes. These tumors are usually
benign but on rare occasions may be malignant.
Benign phyllodes tumors are treated by removing the tumor along with a margin of
normal breast tissue. A malignant phyllodes tumor is treated by removing it along with a
wider margin of normal tissue, or by mastectomy. Surgery is often all that is needed, but
these cancers might not respond as well to the other treatments used for more common
breast cancers. When a malignant phyllodes tumor has spread, it can be treated with the
chemotherapy given for soft-tissue sarcomas. See our document Sarcoma - Adult Soft
Tissue Cancer.
Angiosarcoma
This form of cancer starts in cells that line blood vessels or lymph vessels. It rarely
occurs in the breasts. When it does, it usually develops as a complication of previous
radiation treatments. This is an extremely rare complication of breast radiation therapy
that can develop about 5 to 10 years after radiation. Angiosarcoma can also occur in the
arms of women who develop lymphedema as a result of lymph node surgery or radiation
therapy to treat breast cancer. (For information on lymphedema, see the section "How is
breast cancer treated?") These cancers tend to grow and spread quickly. Treatment is
generally the same as for other sarcomas. See our document Sarcoma - Adult Soft Tissue
Cancer.
This form of cancer starts in cells that line blood vessels or lymph vessels. It rarely
occurs in the breasts. When it does, it usually develops as a complication of previous
radiation treatments. This is an extremely rare complication of breast radiation therapy
that can develop about 5 to 10 years after radiation. Angiosarcoma can also occur in the
arms of women who develop lymphedema as a result of lymph node surgery or radiation
therapy to treat breast cancer. (For information on lymphedema, see the section "How is
breast cancer treated?") These cancers tend to grow and spread quickly. Treatment is
generally the same as for other sarcomas. See our document Sarcoma - Adult Soft Tissue
Cancer.
Special types of invasive breast carcinoma
There are some special types of breast cancer that are sub-types of invasive carcinoma.
These are often named after features seen when they are viewed under the microscope,
like the ways the cells are arranged.
Some of these may have a better prognosis than standard infiltrating ductal carcinoma.
These include:
There are some special types of breast cancer that are sub-types of invasive carcinoma.
These are often named after features seen when they are viewed under the microscope,
like the ways the cells are arranged.
Some of these may have a better prognosis than standard infiltrating ductal carcinoma.
These include:
· Adenoid cystic (or adenocystic) carcinoma
· Low-grade adenosquamous carcinoma (this is a type of metaplastic carcinoma)
· Medullary carcinoma
· Mucinous (or colloid) carcinoma
· Papillary carcinoma
· Tubular carcinoma
Some sub-types have the same or maybe worse prognosis than standard infiltrating ductal
carcinoma. These include:
· Metaplastic carcinoma (most types, including spindle cell and squamous)
· Micropapillary carcinoma
· Mixed carcinoma (has features of both invasive ductal and lobular)
In general, all of these sub-types are still treated like standard infiltrating ductal
carcinoma.
What are the risk factors for breast cancer?
A risk factor is anything that affects your chance of getting a disease, such as cancer.
Different cancers have different risk factors. For example, exposing skin to strong
sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung,
mouth, larynx (voice box), bladder, kidney, and several other organs.
But risk factors don't tell us everything. Having a risk factor, or even several, does not
mean that you will get the disease. Most women who have one or more breast cancer risk
factors never develop the disease, while many women with breast cancer have no
apparent risk factors (other than being a woman and growing older). Even when a woman
with risk factors develops breast cancer, it is hard to know just how much these factors
might have contributed.
Some risk factors, like a person's age or race, can't be changed. Others are linked to
cancer-causing factors in the environment. Still others are related to personal behaviors,
such as smoking, drinking, and diet. Some factors influence risk more than others, and
your risk for breast cancer can change over time, due to factors such as aging or lifestyle.
A risk factor is anything that affects your chance of getting a disease, such as cancer.
Different cancers have different risk factors. For example, exposing skin to strong
sunlight is a risk factor for skin cancer. Smoking is a risk factor for cancers of the lung,
mouth, larynx (voice box), bladder, kidney, and several other organs.
But risk factors don't tell us everything. Having a risk factor, or even several, does not
mean that you will get the disease. Most women who have one or more breast cancer risk
factors never develop the disease, while many women with breast cancer have no
apparent risk factors (other than being a woman and growing older). Even when a woman
with risk factors develops breast cancer, it is hard to know just how much these factors
might have contributed.
Some risk factors, like a person's age or race, can't be changed. Others are linked to
cancer-causing factors in the environment. Still others are related to personal behaviors,
such as smoking, drinking, and diet. Some factors influence risk more than others, and
your risk for breast cancer can change over time, due to factors such as aging or lifestyle.
Risk factors not related to personal choice
Gender
Simply being a woman is the main risk factor for developing breast cancer. Men can
develop breast cancer, but this disease is about 100 times more common among women
than men. This is probably because men have less of the female hormones estrogen and
progesterone, which can promote breast cancer cell growth
Aging
Your risk of developing breast cancer increases as you get older. About 1 out of 8
invasive breast cancers are found in women younger than 45, while about 2 of 3 invasive
breast cancers are found in women age 55 or older.
Gender
Simply being a woman is the main risk factor for developing breast cancer. Men can
develop breast cancer, but this disease is about 100 times more common among women
than men. This is probably because men have less of the female hormones estrogen and
progesterone, which can promote breast cancer cell growth
Aging
Your risk of developing breast cancer increases as you get older. About 1 out of 8
invasive breast cancers are found in women younger than 45, while about 2 of 3 invasive
breast cancers are found in women age 55 or older.
Genetic risk factors
About 5% to 10% of breast cancer cases are thought to be hereditary, meaning that they
result directly from gene defects (called mutations) inherited from a parent. See the
section "Do we know what causes breast cancer?" for more information about genes and
DNA and how they can affect breast cancer risk.
BRCA1 and BRCA2: The most common cause of hereditary breast cancer is an inherited
mutation in the BRCA1 and BRCA2 genes. In normal cells, these genes help prevent
cancer by making proteins that keep the cells from growing abnormally. If you have
inherited a mutated copy of either gene from a parent, you have a high risk of developing
breast cancer during your lifetime.
Although in some families with BRCA1 mutations the lifetime risk of breast cancer is as
high as 80%, on average this risk seems to be in the range of 55 to 65%. For BRCA2
mutations the risk is lower, around 45%.
Breast cancers linked to these mutations occur more often in younger women and more
often affect both breasts than cancers not linked to these mutations. Women with these
inherited mutations also have an increased risk for developing other cancers, particularly
ovarian cancer.
In the United States BRCA mutations are more common in Jewish people of Ashkenazi
(Eastern Europe) origin than in other racial and ethnic groups, but they can occur in
anyone.
About 5% to 10% of breast cancer cases are thought to be hereditary, meaning that they
result directly from gene defects (called mutations) inherited from a parent. See the
section "Do we know what causes breast cancer?" for more information about genes and
DNA and how they can affect breast cancer risk.
BRCA1 and BRCA2: The most common cause of hereditary breast cancer is an inherited
mutation in the BRCA1 and BRCA2 genes. In normal cells, these genes help prevent
cancer by making proteins that keep the cells from growing abnormally. If you have
inherited a mutated copy of either gene from a parent, you have a high risk of developing
breast cancer during your lifetime.
Although in some families with BRCA1 mutations the lifetime risk of breast cancer is as
high as 80%, on average this risk seems to be in the range of 55 to 65%. For BRCA2
mutations the risk is lower, around 45%.
Breast cancers linked to these mutations occur more often in younger women and more
often affect both breasts than cancers not linked to these mutations. Women with these
inherited mutations also have an increased risk for developing other cancers, particularly
ovarian cancer.
In the United States BRCA mutations are more common in Jewish people of Ashkenazi
(Eastern Europe) origin than in other racial and ethnic groups, but they can occur in
anyone.
Changes in other genes: Other gene mutations can also lead to inherited breast cancers.
These gene mutations are much rarer and often do not increase the risk of breast cancer as
much as the BRCA genes. They are not frequent causes of inherited breast cancer.
These gene mutations are much rarer and often do not increase the risk of breast cancer as
much as the BRCA genes. They are not frequent causes of inherited breast cancer.
- ATM: The ATM gene normally helps repair damaged DNA. Inheriting 2 abnormal
copies of this gene causes the disease ataxia-telangiectasia. Inheriting 1 mutated copy
of this gene has been linked to a high rate of breast cancer in some families.
of this gene has been linked to a high rate of breast cancer in some families.
- TP53: The TP53 gene gives instructions for making a protein called p53 that helps
stop the growth of abnormal cells. Inherited mutations of this gene cause Li-Fraumeni
syndrome (named after the 2 researchers who first described it). People with this
syndrome have an increased risk of developing breast cancer, as well as several other
cancers such as leukemia, brain tumors, and sarcomas (cancer of bones or connective
tissue). This is a rare cause of breast cancer.
syndrome (named after the 2 researchers who first described it). People with this
syndrome have an increased risk of developing breast cancer, as well as several other
cancers such as leukemia, brain tumors, and sarcomas (cancer of bones or connective
tissue). This is a rare cause of breast cancer.
- CHEK2: The Li-Fraumeni syndrome can also be caused by inherited mutations in the
CHEK2 gene. Even when it does not cause this syndrome, it can increase breast
cancer risk about twofold when it is mutated.
cancer risk about twofold when it is mutated.
- PTEN: The PTEN gene normally helps regulate cell growth. Inherited mutations in
this gene can cause Cowden syndrome, a rare disorder in which people are at
increased risk for both benign and malignant breast tumors, as well as growths in the
digestive tract, thyroid, uterus, and ovaries. Defects in this gene can also cause a
different syndrome called Bannayan-Riley-Ruvalcaba syndrome that is not thought to
be linked to breast cancer risk. Recently, the syndromes caused by PTEN have been
combined into one called PTEN Tumor Hamartoma Syndrome.
increased risk for both benign and malignant breast tumors, as well as growths in the
digestive tract, thyroid, uterus, and ovaries. Defects in this gene can also cause a
different syndrome called Bannayan-Riley-Ruvalcaba syndrome that is not thought to
be linked to breast cancer risk. Recently, the syndromes caused by PTEN have been
combined into one called PTEN Tumor Hamartoma Syndrome.
- CDH1: Inherited mutations in this gene cause hereditary diffuse gastric cancer, a
syndrome in which people develop a rare type of stomach cancer at an early age.
Women with mutations in this gene also have an increased risk of invasive lobular
breast cancer.
Women with mutations in this gene also have an increased risk of invasive lobular
breast cancer.
- STK11: Defects in this gene can lead to Peutz-Jeghers syndrome. People with this
disorder develop pigmented spots on their lips and in their mouths, polyps in the
urinary and gastrointestinal tracts, and have an increased risk of many types of
cancer, including breast cancer.
urinary and gastrointestinal tracts, and have an increased risk of many types of
cancer, including breast cancer.
- PALB2: The PALB2 gene makes a protein that interacts with the protein made by the
BRCA2 gene. Defects (mutations) in this gene can lead to an increased risk of breast
cancer. It isn’t yet clear if PALB2 gene mutations also increase the risk for ovarian
cancer and male breast cancer.
cancer. It isn’t yet clear if PALB2 gene mutations also increase the risk for ovarian
cancer and male breast cancer.
Genetic testing: Genetic tests can be done to look for mutations in the BRCA1 and
BRCA2 genes (or some other genes linked to breast cancer risk). Although testing may be
helpful in some situations, the pros and cons need to be considered carefully. For more
information, see the section "Can breast cancer be prevented?"
Family history of breast cancer
Breast cancer risk is higher among women whose close blood relatives have this disease.
Having one first-degree relative (mother, sister, or daughter) with breast cancer
approximately doubles a woman's risk. Having 2 first-degree relatives increases her risk
about 3-fold.
The exact risk is not known, but women with a family history of breast cancer in a father
or brother also have an increased risk of breast cancer. Altogether, less than 15% of
women with breast cancer have a family member with this disease. This means that most
(over 85%) women who get breast cancer do not have a family history of this disease.
Breast cancer risk is higher among women whose close blood relatives have this disease.
Having one first-degree relative (mother, sister, or daughter) with breast cancer
approximately doubles a woman's risk. Having 2 first-degree relatives increases her risk
about 3-fold.
The exact risk is not known, but women with a family history of breast cancer in a father
or brother also have an increased risk of breast cancer. Altogether, less than 15% of
women with breast cancer have a family member with this disease. This means that most
(over 85%) women who get breast cancer do not have a family history of this disease.
Personal history of breast cancer
A woman with cancer in one breast has a 3- to 4-fold increased risk of developing a new
cancer in the other breast or in another part of the same breast. This is different from a
recurrence (return) of the first cancer.
A woman with cancer in one breast has a 3- to 4-fold increased risk of developing a new
cancer in the other breast or in another part of the same breast. This is different from a
recurrence (return) of the first cancer.
Race and ethnicity
Overall, white women are slightly more likely to develop breast cancer than are African-
American women, but African-American women are more likely to die of this cancer.
However, in women under 45 years of age, breast cancer is more common in African-
American women. Asian, Hispanic, and Native-American women have a lower risk of
developing and dying from breast cancer.
Dense breast tissue
Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. Someone is said
to have dense breast tissue (as seen on a mammogram) when they have more glandular
and fibrous tissue and less fatty tissue. Women with dense breasts on mammogram have
a risk of breast cancer that is 1.2 to 2 times that of women with average breast density.
Unfortunately, dense breast tissue can also make mammograms less accurate.
A number of factors can affect breast density, such as age, menopausal status, certain
medications (including menopausal hormone therapy), pregnancy, and genetics.
Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. Someone is said
to have dense breast tissue (as seen on a mammogram) when they have more glandular
and fibrous tissue and less fatty tissue. Women with dense breasts on mammogram have
a risk of breast cancer that is 1.2 to 2 times that of women with average breast density.
Unfortunately, dense breast tissue can also make mammograms less accurate.
A number of factors can affect breast density, such as age, menopausal status, certain
medications (including menopausal hormone therapy), pregnancy, and genetics.
Certain benign breast conditions
Women diagnosed with certain benign breast conditions might have an increased risk of
breast cancer. Some of these conditions are more closely linked to breast cancer risk than
others. Doctors often divide benign breast conditions into 3 general groups, depending on
how they affect this risk.
Non-proliferative lesions: These conditions are not associated with overgrowth of breast
tissue. They do not seem to affect breast cancer risk, or if they do, it is to a very small
extent. They include:
· Fibrosis and/or simple cysts (this used to be called fibrocystic disease or changes)
· Mild hyperplasia
· Adenosis (non-sclerosing)
· Ductal ectasia
· Phyllodes tumor (benign)
· A single papilloma
· Fat necrosis
· Periductal fibrosis
· Squamous and apocrine metaplasia
· Epithelial-related calcifications
· Other benign tumors (lipoma, hamartoma, hemangioma, neurofibroma,
adenomyoepthelioma)
Mastitis (infection of the breast) is not a lesion, but is a condition that can occur that does
not increase the risk of breast cancer.
Proliferative lesions without atypia: These conditions show excessive growth of cells
in the ducts or lobules of the breast tissue. They seem to raise a woman's risk of breast
cancer slightly (1½ to 2 times normal). They include:
· Usual ductal hyperplasia (without atypia)
· Fibroadenoma
· Sclerosing adenosis
· Several papillomas (called papillomatosis)
· Radial scar
Proliferative lesions with atypia: In these conditions, there is an overgrowth of cells in
the ducts or lobules of the breast tissue, with some of the cells no longer appearing
normal. They have a stronger effect on breast cancer risk, raising it 3½ to 5 times higher
than normal. These types of lesions include:
· Atypical ductal hyperplasia (ADH)
· Atypical lobular hyperplasia (ALH)
Women with a family history of breast cancer and either hyperplasia or atypical
hyperplasia have an even higher risk of developing a breast cancer.
Lobular carcinoma in situ
In lobular carcinoma in situ (LCIS) cells that look like cancer cells are growing in the
lobules of the milk-producing glands of the breast, but they do not grow through the wall
of the lobules. LCIS (also called lobular neoplasia) is sometimes grouped with ductal
carcinoma in situ (DCIS) as a non-invasive breast cancer, but it differs from DCIS in that
it doesn’t seem to become an invasive cancer if it isn’t treated.
tissue. They do not seem to affect breast cancer risk, or if they do, it is to a very small
extent. They include:
· Fibrosis and/or simple cysts (this used to be called fibrocystic disease or changes)
· Mild hyperplasia
· Adenosis (non-sclerosing)
· Ductal ectasia
· Phyllodes tumor (benign)
· A single papilloma
· Fat necrosis
· Periductal fibrosis
· Squamous and apocrine metaplasia
· Epithelial-related calcifications
· Other benign tumors (lipoma, hamartoma, hemangioma, neurofibroma,
adenomyoepthelioma)
Mastitis (infection of the breast) is not a lesion, but is a condition that can occur that does
not increase the risk of breast cancer.
Proliferative lesions without atypia: These conditions show excessive growth of cells
in the ducts or lobules of the breast tissue. They seem to raise a woman's risk of breast
cancer slightly (1½ to 2 times normal). They include:
· Usual ductal hyperplasia (without atypia)
· Fibroadenoma
· Sclerosing adenosis
· Several papillomas (called papillomatosis)
· Radial scar
Proliferative lesions with atypia: In these conditions, there is an overgrowth of cells in
the ducts or lobules of the breast tissue, with some of the cells no longer appearing
normal. They have a stronger effect on breast cancer risk, raising it 3½ to 5 times higher
than normal. These types of lesions include:
· Atypical ductal hyperplasia (ADH)
· Atypical lobular hyperplasia (ALH)
Women with a family history of breast cancer and either hyperplasia or atypical
hyperplasia have an even higher risk of developing a breast cancer.
Lobular carcinoma in situ
In lobular carcinoma in situ (LCIS) cells that look like cancer cells are growing in the
lobules of the milk-producing glands of the breast, but they do not grow through the wall
of the lobules. LCIS (also called lobular neoplasia) is sometimes grouped with ductal
carcinoma in situ (DCIS) as a non-invasive breast cancer, but it differs from DCIS in that
it doesn’t seem to become an invasive cancer if it isn’t treated.
Women with this condition have a 7- to 11-fold increased risk of developing invasive
cancer in either breast. For this reason, women with LCIS should make sure they have
regular mammograms and doctor visits.
Menstrual periods
Women who have had more menstrual cycles because they started menstruating early
(before age 12) and/or went through menopause later (after age 55) have a slightly higher
risk of breast cancer. The increase in risk may be due to a longer lifetime exposure to the
hormones estrogen and progesterone.
Previous chest radiation
Women who, as children or young adults, had radiation therapy to the chest area as
treatment for another cancer (such as lymphoma) have a significantly increased risk for
breast cancer. This varies with the patient's age when they had radiation. If chemotherapy
was also given, it may have stopped ovarian hormone production for some time, lowering
the risk. The risk of developing breast cancer from chest radiation is highest if the
radiation was given during adolescence, when the breasts were still developing. Radiation
treatment after age 40 does not seem to increase breast cancer risk.
Diethylstilbestrol exposure
From the 1940s through the 1960s some pregnant women were given the drug
diethylstilbestrol (DES) because it was thought to lower their chances of miscarriage
(losing the baby). These women have a slightly increased risk of developing breast
cancer. Women whose mothers took DES during pregnancy may also have a slightly
higher risk of breast cancer. For more information on DES see our document DES
Exposure: Questions and Answers.
Lifestyle-related factors and breast cancer risk
Having children
Women who have had no children or who had their first child after age 30 have a slightly
higher breast cancer risk overall. Having many pregnancies and becoming pregnant at a
young age reduce breast cancer risk overall. Still, the effect of pregnancy is different for
different types of breast cancer. For a certain type of breast cancer known as triplenegative,
pregnancy seems to increase risk.
Birth control
Oral contraceptives: Studies have found that women using oral contraceptives (birth
control pills) have a slightly greater risk of breast cancer than women who have never
used them. This risk seems to go back to normal over time once the pills are stopped.
Women who stopped using oral contraceptives more than 10 years ago do not appear to
have any increased breast cancer risk. When thinking about using oral contraceptives,
women should discuss their other risk factors for breast cancer with their health care
team.
Depot-medroxyprogesterone acetate (DMPA; Depo-Provera®) is an injectable form of
progesterone that is given once every 3 months as birth control. A few studies have
looked at the effect of DMPA on breast cancer risk. Women currently using DMPA seem
to have an increase in risk, but the risk doesn’t seem to be increased if this drug was used
more than 5 years ago.
Hormone therapy after menopause
Hormone therapy with estrogen (often combined with progesterone) has been used for
many years to help relieve symptoms of menopause and to help prevent osteoporosis
(thinning of the bones). Earlier studies suggested it might have other health benefits as
well, but these benefits have not been found in more recent, better designed studies. This
treatment goes by many names, such as post-menopausal hormone therapy (PHT),
hormone replacement therapy (HRT), and menopausal hormone therapy (MHT).
There are 2 main types of hormone therapy. For women who still have a uterus (womb),
doctors generally prescribe both estrogen and progesterone (known as combined hormone
therapy or HT). Progesterone is needed because estrogen alone can increase the risk of
cancer of the uterus. For women who no longer have a uterus (those who've had a
hysterectomy), estrogen alone can be prescribed. This is commonly known as estrogen
replacement therapy (ERT) or just estrogen therapy (ET).
Studies have shown that using combined hormone therapy after menopause increases the
risk of getting breast cancer. It may also increase the chances of dying from breast
cancer.
The use of estrogen alone after menopause does not appear to increase the risk of
developing breast cancer.
For more information about this topic, see our document Menopausal Hormone Therapy.
Breastfeeding
Some studies suggest that breastfeeding may slightly lower breast cancer risk, especially
if it is continued for 1½ to 2 years. But this has been a difficult area to study, especially in
countries such as the United States, where breastfeeding for this long is uncommon.
One explanation for this possible effect may be that breastfeeding reduces a woman's
total number of lifetime menstrual cycles (similar to starting menstrual periods at a later
age or going through early menopause).
Drinking alcohol
The use of alcohol is clearly linked to an increased risk of developing breast cancer. The
risk increases with the amount of alcohol consumed. Compared with non-drinkers,
women who consume 1 alcoholic drink a day have a very small increase in risk. Those
who have 2 to 5 drinks daily have about 1½ times the risk of women who don’t drink
alcohol. Excessive alcohol consumption is also known to increase the risk of developing
several other types of cancer.
Being overweight or obese
Being overweight or obese after menopause increases breast cancer risk. Before
menopause your ovaries produce most of your estrogen, and fat tissue produces a small
amount of estrogen. After menopause (when the ovaries stop making estrogen), most of a
woman's estrogen comes from fat tissue. Having more fat tissue after menopause can
increase your chance of getting breast cancer by raising estrogen levels. Also, women
who are overweight tend to have higher blood insulin levels. Higher insulin levels have
also been linked to some cancers, including breast cancer.
But the connection between weight and breast cancer risk is complex. For example, the
risk appears to be increased for women who gained weight as an adult but may not be
increased among those who have been overweight since childhood. Also, excess fat in the
waist area may affect risk more than the same amount of fat in the hips and thighs.
Researchers believe that fat cells in various parts of the body have subtle differences that
may explain this.
Physical activity
Evidence is growing that physical activity in the form of exercise reduces breast cancer
risk. The main question is how much exercise is needed. In one study from the Women's
Health Initiative, as little as 1.25 to 2.5 hours per week of brisk walking reduced a
woman's risk by 18%. Walking 10 hours a week reduced the risk a little more.
Unclear factors
Diet and vitamin intake
Many studies have looked for a link between what women eat and breast cancer risk, but
so far the results have been conflicting. Some studies have indicated that diet may play a
role, while others found no evidence that diet influences breast cancer risk. For example,
a recent study found a higher risk of breast cancer in women who ate more red meat.
Studies have also looked at vitamin levels, again with inconsistent results. Some studies
actually found an increased risk of breast cancer in women with higher levels of certain
nutrients. So far, no study has shown that taking vitamins reduces breast cancer risk. This
is not to say that there is no point in eating a healthy diet. A diet low in fat, low in red
meat and processed meat, and high in fruits and vegetables might have other health
benefits.
Most studies have found that breast cancer is less common in countries where the typical
diet is low in total fat, low in polyunsaturated fat, and low in saturated fat. But many
studies of women in the United States have not linked breast cancer risk to dietary fat
intake. Researchers are still not sure how to explain this apparent disagreement. It may be
at least partly due to the effect of diet on body weight (see below). Also, studies
comparing diet and breast cancer risk in different countries are complicated by other
differences (like activity level, intake of other nutrients, and genetic factors) that might
also affect breast cancer risk.
More research is needed to understand the effect of the types of fat eaten on breast cancer
risk. But it is clear that calories do count, and fat is a major source of calories. High-fat
diets can lead to being overweight or obese, which is a breast cancer risk factor. A diet
high in fat has also been shown to influence the risk of developing several other types of
cancer, and intake of certain types of fat is clearly related to heart disease risk.
Chemicals in the environment
A great deal of research has been reported and more is being done to understand possible
environmental influences on breast cancer risk.
Compounds in the environment that have estrogen-like properties are of special interest.
For example, substances found in some plastics, certain cosmetics and personal care
products, pesticides (such as DDE), and PCBs (polychlorinated biphenyls) seem to have
such properties. These could in theory affect breast cancer risk.
This issue understandably invokes a great deal of public concern, but at this time research
does not show a clear link between breast cancer risk and exposure to these substances.
Unfortunately, studying such effects in humans is difficult. More research is needed to
better define the possible health effects of these and similar substances.
Tobacco smoke
For a long time, studies found no link between cigarette smoking and breast cancer. In
recent years though, more studies have found that long-term heavy smoking is linked to a
higher risk of breast cancer. Some studies have found that the risk is highest in certain
groups, such as women who started smoking before they had their first child. The 2014
US Surgeon General’s report on smoking concluded that there is “suggestive but not
sufficient” evidence that smoking increases the risk of breast cancer.
An active focus of research is whether secondhand smoke increases the risk of breast
cancer. Both mainstream and secondhand smoke contain chemicals that, in high
concentrations, cause breast cancer in rodents. Chemicals in tobacco smoke reach breast
tissue and are found in breast milk.
The evidence on secondhand smoke and breast cancer risk in human studies is
controversial, at least in part because the link between smoking and breast cancer hasn’t
been clear. One possible explanation for this is that tobacco smoke may have different
effects on breast cancer risk in smokers and in those who are just exposed to smoke.
A report from the California Environmental Protection Agency in 2005 concluded that
the evidence about secondhand smoke and breast cancer is “consistent with a causal
association” in younger, mainly premenopausal women. The 2014 US Surgeon General’s
report concluded that there is “suggestive but not sufficient” evidence of a link at this
point. In any case, this possible link to breast cancer is yet another reason to avoid
secondhand smoke.
Night work
Several studies have suggested that women who work at night—for example, nurses on a
night shift—may have an increased risk of developing breast cancer. This is a fairly
recent finding, and more studies are looking at this issue. Some researchers think the
effect may be due to changes in levels of melatonin, a hormone whose production is
affected by the body's exposure to light, but other hormones are also being studied.
Controversial or disproven factors
Antiperspirants
Internet and e-mail rumors have suggested that chemicals in underarm antiperspirants are
absorbed through the skin, interfere with lymph circulation, cause toxins to build up in
the breast, and eventually lead to breast cancer.
Based on the available evidence (including what we know about how the body works),
there is little if any reason to believe that antiperspirants increase the risk of breast
cancer. For more information about this, see our document Antiperspirants and Breast
Cancer Risk.
Bras
Internet and e-mail rumors and at least one book have suggested that bras cause breast
cancer by obstructing lymph flow. There is no good scientific or clinical basis for this
claim, and a recent study of more than 1,500 women found no association of bra use with
breast cancer risk.
Induced abortion
Several studies have provided very strong data that neither induced abortions nor
spontaneous abortions (miscarriages) have an overall effect on the risk of breast cancer.
For more detailed information, see our document Is Abortion Linked to Breast Cancer?
Breast implants
Several studies have found that breast implants do not increase the risk of breast cancer,
although silicone breast implants can cause scar tissue to form in the breast. Implants
make it harder to see breast tissue on standard mammograms, but additional x-ray
pictures called implant displacement views can be used to examine the breast tissue more
completely.
Breast implants may be linked to a rare type of lymphoma called anaplastic large cell
lymphoma. This lymphoma has rarely been found in the breast tissue around the implants.
So far, though, there are too few cases to know if the risk of this lymphoma is really
higher in women that have implants.
Breast Cancer Treatment Protocols
Stage 0, I, II or IIIA (T3N1M0)
In the United States and other developed nations where screening is performed, most patients present with localized breast cancer that is detected by a screening mammogram; less commonly, patients present with a palpable mass that is either self-detected or detected by a health care provider.Stage 0 (lobular carcinoma in situ [LCIS])
- Management options include surveillance alone (ie, mammography), surveillance plus raloxifene (for postmenopausal women) or tamoxifen (for women of any menopausal status), or bilateral prophylactic mastectomy (usually in patients who are very concerned about breast cancer risk and have either a strong family history or mammographically dense breasts that impair surveillance)
- If LCIS is detected on stereotactic biopsy, wide excision is indicated, which in 10-20% of cases may reveal invasive cancer or ductal carcinoma in situ (DCIS) that requires additional local or systemic therapy.
- Surgical excision to negative margins is not indicated; however, LCIS is associated with about a 5% 5-y risk and a 20-30% lifetime risk of developing invasive breast cancer, which may be ipsilateral or contralateral and may be ductal or lobular in origin.
Stage 0 (ductal carcinoma in situ [DCIS])
- Primary treatment options include lumpectomy without axillary dissection plus whole-breast radiation therapy (RT); use of radiation boost (photons, brachytherapy, or electron beam) to the tumor bed is recommended, especially in patients ≥ 50y or
- Total mastectomy, with or without sentinel node biopsy (SNB) and with or without breast reconstruction or
- Lumpectomy without lymph node surgery and without radiation therapy (lower-level evidence)
- Although axillary dissection or SNB is often not performed, SNB may be done in some cases if an initial core biopsy showed DCIS, because more extensive sampling may show invasive carcinoma
- In the absence of risk factors for recurrence (palpable mass, larger size, higher grade, close or involved margins, age < 50 y), some patients may not receive RT
- Consider risk-reduction therapy with tamoxifen for 5y for patients treated with lumpectomy and RT, especially those with estrogen receptor (ER)–positive DCIS
Stage I, IIA, IIB, or IIIA (T3N1M0)
- Treatment consists of surgery; RT in most cases; and adjuvant chemotherapy, endocrine therapy, or biologic therapy in some cases
- Surgical treatment is with excision or mastectomy, axillary dissection, SNB, or SNB followed by axillary dissection
- RT is used in patients who undergo wide excision or, in selected cases, after mastectomy; treatment fields are determined by axillary node status
- RT should follow chemotherapy if chemotherapy is indicated
- If patients have ≥ 4 positive axillary nodes, whole-breast RT, with or without boost to the tumor bed, is recommended; RT to the infraclavicular and supraclavicular areas should also be considered
- Patients with 1-3 positive axillary nodes should also receive whole-breast RT, with or without boost to the tumor bed; RT to the infraclavicular and supraclavicular areas should also be considered, as should RT to internal mammary nodes
- Patients with negative axillary nodes should receive RT to the whole breast, with or without boost to the tumor bed; partial breast irradiation (PBI) may be considered in selected patients
- Patients with ≥ 4 positive axillary nodes should receive postchemotherapy RT to the chest wall plus the infraclavicular and supraclavicular areas; consider RT to internal mammary nodes
- For patients with 1-3 positive axillary nodes, consider postchemotherapy RT to the chest wall, with or without infraclavicular and supraclavicular nodes; consider RT to internal mammary nodes
- For patients with negative axillary nodes and tumor > 5 cm or positive margins, consider RT to the chest wall, with or without infraclavicular and supraclavicular nodes; consider RT to internal mammary nodes
- For patients with negative axillary nodes, tumor ≤ 5 cm, and margins < 1 mm, postchemotherapy RT to the chest wall is recommended
- For patients who have negative axillary nodes, tumor ≤ 5 cm, and margins ≥ 1 mm, no RT is needed
- Preoperative chemotherapy should be considered for women who meet criteria for breast-conserving therapy (except size)
- If the patient has clinically negative axillary nodes, consider SNB; if the patient has positive axillary nodes, consider a core biopsy or fine-needle aspiration (FNA), then SNB if FNA or core biopsy is negative
- TAC: Docetaxel 75 mg/m2 IV on day 1 plus doxorubicin 50 mg/m2 IV on day 1 plus cyclophosphamide 500 mg/m2 IV on day 1 every 3wk for 6 cycles or
- Dose-dense ACP: Doxorubicin 60 mg/m2 IV plus cyclophosphamide 600 mg/m2 every 2wk for 4 cycles; followed by paclitaxel 175 mg/m2 every 2wk with colony-stimulating factor (CSF) support (more effective than the 3-wk schedule in ER-negative or progesterone receptor (PR)-negative disease) or
- AC: Doxorubicin 60 mg/m2 IV plus cyclophosphamide 600 mg/m2 IV on day 1 every 3wk for 4 cycles (comparable to CMF [cyclophosphamide, methotrexate, fluorouracil])or
- TC: Docetaxel 75 mg/m2 IV on day 1 plus cyclophosphamide 600 mg/m2 IV on day 1 every 3wk for 4 cycles.Réferences :
- American cancer society
