What is breast cancer?

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.

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).

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 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.

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 those 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 that have breast cancer, 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.

Benign breast lumps

Most breast lumps are not cancerous (benign). Still, some may need to be sampled and viewed under a microscope to prove they are not cancer.

Fibrocystic changes

Most lumps turn out to be fibrocystic changes. The term fibrocystic refers to fibrosis and cysts. Fibrosis is the formation of scar-like (fibrous) tissue, and cysts are fluid-filled sacs. Fibrocystic changes can cause breast swelling and pain. This often happens just before a woman's menstrual period is about to begin. Her breasts may feel lumpy and, sometimes, she may notice a clear or slightly cloudy nipple discharge.

Other benign breast lumps

Benign breast tumors such as fibroadenomas or intraductal papillomas are abnormal growths, but they are not cancerous and do not spread outside the breast to other organs. They are not life threatening. Still, some benign breast conditions are important because women with these conditions have a higher risk of developing breast cancer.

For more information see the section, "What are the risk factors for breast cancer?" and our document, Non-cancerous Breast Conditions.

General breast cancer terms

Here are some of the key words used to describe breast cancer.

Carcinoma

This is a term used to describe a cancer that begins in the lining layer (epithelial cells) of organs like the breast. Nearly all breast cancers are carcinomas (either ductal carcinomas or lobular carcinomas).

Adenocarcinoma

An adenocarcinoma is a type of carcinoma that starts in glandular tissue (tissue that makes and secretes a substance). The ducts and lobules of the breast are glandular tissue (they make breast milk), so cancers starting in these areas are often called adenocarcinomas.

Carcinoma in situ

This term is used for an early stage of cancer, when it is confined to the layer of cells where it began. In breast cancer, in situmeans that the cancer cells remain confined to ducts (ductal carcinoma in situ). The cells have not grown into (invaded) deeper tissues in the breast or spread to other organs in the body. Carcinoma in situ of the breast is sometimes referred to as non-invasive or pre-invasive breast cancer because it may develop into an invasive breast cancer if left untreated.

When cancer cells are confined to the lobules it is called lobular carcinoma in situ). This is not actually a true cancer or pre-cancer, and is discussed more in the section, “What are the risk factors for breast cancer?”

Invasive (infiltrating) carcinoma

An invasive cancer is one that has already grown beyond the layer of cells where it started (as opposed to carcinoma in situ). Most breast cancers are invasive carcinomas — either invasive ductal carcinoma or invasive lobular carcinoma.

Sarcoma

Sarcomas are cancers that start in connective tissues such as muscle tissue, fat tissue, or blood vessels. Sarcomas of the breast are rare.

Types of breast cancers

There are several types of breast cancer, but some of them are quite rare. In some cases a single breast tumor can be a combination of these types or be a mixture of invasive and in situ cancer.

Ductal carcinoma in situ

Ductal carcinoma in situ (DCIS; also known as intraductal carcinoma) is the most common type of non-invasive breast cancer. DCIS means that the cancer cells are inside the ducts but have not spread through the walls of the ducts into the surrounding breast tissue.

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. A mammogram is often the best way to find DCIS early.

When DCIS is diagnosed, the pathologist (a doctor specializing in diagnosing disease from tissue samples) will look for areas of dead or dying cancer cells, called tumor necrosis, within the tissue sample. If necrosis is present, the tumor is likely to be more aggressive. The term comedocarcinoma is often used to describe DCIS with necrosis.

Lobular carcinoma in situ

This is not a true cancer or pre-cancer, and is discussed in the section “What are the risk factors for breast cancer?”

Invasive (or infiltrating) ductal carcinoma

This is the most common type of breast cancer. Invasive (or infiltrating) ductal carcinoma (IDC) starts in a milk passage (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.

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 of 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). Often this cancer is first 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 may not show up on a mammogram, which may 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.

Triple-negative breast cancer: This term is used to describe breast cancers (usually invasive ductal carcinomas) whose cells lack estrogen receptors and progesterone receptors, and do not have an excess of the HER2 protein on their surfaces. (See the section, "How is breast cancer diagnosed?" for more detail on these receptors.) Breast cancers with these characteristics tend to occur more often in younger women and in African-American women. Triple-negative breast cancers tend to grow and spread more quickly than most other types of breast cancer. Because the tumor cells lack these certain receptors, neither hormone therapy nor drugs that target HER2 are effective treatments (but chemotherapy can still be useful if needed).

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.

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 andcystosarcoma 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 may 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 (this is discussed in detail in our document, Soft-tissue Sarcomas.

Angiosarcoma: This is a form of cancer that 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:

• 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.

Breast cancer

Cancer - breast; Carcinoma - ductal; Carcinoma - lobular; DCIS; LCIS; HER2-positive breast cancer; ER-positive breast cancer; Ductal carcinoma in situ; Lobular carcinoma in situ

Breast cancer is a cancer that starts in the tissues of the breast. There are two main types of breast cancer:

• Ductal carcinoma starts in the tubes (ducts) that move milk from the breast to the nipple. Most breast cancers are of this type.
• Lobular carcinoma starts in the parts of the breast, called lobules, that produce milk.

In rare cases, breast cancer can start in other areas of the breast.

Breast cancer may be invasive or noninvasive. Invasive means it has spread from the milk duct or lobule to other tissues in the breast. Noninvasive means it has not yet invaded other breast tissue. Noninvasive breast cancer is called "in situ."

• Ductal carcinoma in situ (DCIS), or intraductal carcinoma, is breast cancer in the lining of the milk ducts that has not yet invaded nearby tissues. It may progress to invasive cancer if untreated.
• Lobular carcinoma in situ (LCIS) is a marker for an increased risk of invasive cancer in the same or both breasts.

Many breast cancers are sensitive to the hormone estrogen. This means that estrogen causes the breast cancer tumor to grow. Such cancers have estrogen receptors on the surface of their cells. They are called estrogen receptor-positive cancer or ER-positive cancer.

Some women have what is called HER2-positive breast cancer. HER2 refers to a gene that helps cells grow, divide, and repair themselves. When cells (including cancer cells) have too many copies of this gene, they grow faster. Historically, women with HER2-positive breast cancer have a more aggressive disease and a higher risk that the disease will return (recur) than women who do not have this type. However, this may be changing with specifically targeted treatments against HER2.

Causes, incidence, and risk factors

Over the course of a lifetime, 1 in 8 women will be diagnosed with breast cancer.

Risk factors you cannot change include:

• Age and gender -- Your risk of developing breast cancer increases as you get older. Most advanced breast cancer cases are found in women over age 50. Women are 100 times more likely to get breast cancer than men.
• Family history of breast cancer -- You may also have a higher risk for breast cancer if you have a close relative who has had breast, uterine, ovarian, or colon cancer. About 20 - 30% of women with breast cancer have a family history of the disease.
• Genes -- Some people have genes that make them more likely to develop breast cancer. The most common gene defects are found in the BRCA1 and BRCA2 genes. These genes normally produce proteins that protect you from cancer. If a parent passes you a defective gene, you have an increased risk for breast cancer. Women with one of these defects have up to an 80% chance of getting breast cancer sometime during their life.
• Menstrual cycle -- Women who got their periods early (before age 12) or went through menopause late (after age 55) have an increased risk for breast cancer.

Other risk factors include:

• Alcohol use -- Drinking more than 1 - 2 glasses of alcohol a day may increase your risk for breast cancer.
• Childbirth -- Women who have never had children or who had them only after age 30 have an increased risk for breast cancer. Being pregnant more than once or becoming pregnant at an early age reduces your risk of breast cancer.
• DES -- Women who took diethylstilbestrol (DES) to prevent miscarriage may have an increased risk of breast cancer after age 40. This drug was given to the women in the 1940s - 1960s.
• Hormone replacement therapy (HRT) -- You have a higher risk for breast cancer if you have received hormone replacement therapy with estrogen for several years or more.Obesity -- Obesity has been linked to breast cancer, although this link is controversial. The theory is that obese women produce more estrogen, which can fuel the development of breast cancer.
• Radiation -- If you received radiation therapy as a child or young adult to treat cancer of the chest area, you have a much higher risk for developing breast cancer. The younger you started such radiation and the higher the dose, the higher your risk -- especially if the radiation was given during breast development.

Breast implants, using antiperspirants, and wearing underwire bras do not raise your risk for breast cancer. There is no evidence of a direct link between breast cancer and pesticides.

The National Cancer Institute provides an online tool to help you figure out your risk of breast cancer. See:www.cancer.gov/bcrisktool

Symptoms

Early breast cancer usually does not cause symptoms. This is why regular breast exams are important. As the cancer grows, symptoms may include:

• Breast lump or lump in the armpit that is hard, has uneven edges, and usually does not hurt
• Change in the size, shape, or feel of the breast or nipple -- for example, you may have redness, dimpling, or puckering that looks like the skin of an orange
• Fluid coming from the nipple -- may be bloody, clear to yellow, green, and look like pus

Men can get breast cancer, too. Symptoms include breast lump and breast pain and tenderness.

Symptoms of advanced breast cancer may include:

• Bone pain
• Breast pain or discomfort
• Skin ulcers
• Swelling of one arm (next to the breast with cancer)
• Weight loss

Signs and tests

The doctor will ask you about your symptoms and risk factors. Then the doctor will perform a physical exam, which includes both breasts, armpits, and the neck and chest area.

Tests used to diagnose and monitor patients with breast cancer may include:

• Breast MRI to help better identify the breast lump or evaluate an abnormal change on a mammogram
• Breast ultrasound to show whether the lump is solid or fluid-filled
• Breast biopsy, using methods such as needle aspiration, ultrasound-guided, stereotactic, or open
• CT scan to see if the cancer has spread
• Mammography to screen for breast cancer or help identify the breast lump
• PET scan
• Sentinal lymph node biopsy to see if the cancer has spread

If your doctor learns that you do have breast cancer, more tests will be done to see if the cancer has spread. This is called staging. Staging helps guide future treatment and follow-up and gives you some idea of what to expect in the future.

Breast cancer stages range from 0 to IV. The higher the staging number, the more advanced the cancer.

Treatment

Treatment is based on many factors, including:

• Type and stage of the cancer
• Whether the cancer is sensitive to certain hormones
• Whether the cancer overproduces (overexpresses) a gene called HER2/neu

In general, cancer treatments may include:

• Chemotherapy medicines to kill cancer cells
• Radiation therapy to destroy cancerous tissue
• Surgery to remove cancerous tissue -- a lumpectomy removes the breast lump; mastectomy removes all or part of the breast and possible nearby structures

Hormonal therapy is prescribed to women with ER-positive breast cancer to block certain hormones that fuel cancer growth.

• An example of hormonal therapy is the drug tamoxifen. This drug blocks the effects of estrogen, which can help breast cancer cells survive and grow. Most women with estrogen-sensitive breast cancer benefit from this drug.
• Another class of hormonal therapy medicines called aromatase inhibitors, such as exemestane(Aromasin), have been shown to work just as well or even better than tamoxifen in postmenopausal women with breast cancer. Aromatase inhibitors block estrogen from being made.

Targeted therapy, also called biologic therapy, is a newer type of cancer treatment. This therapy uses special anticancer drugs that target certain changes in a cell that can lead to cancer. One such drug is trastuzumab (Herceptin). It may be used for women with HER2-positive breast cancer.

Cancer treatment may be local or systemic.

• Local treatments involve only the area of disease. Radiation and surgery are forms of local treatment.
• Systemic treatments affect the entire body. Chemotherapy is a type of systemic treatment.

Most women receive a combination of treatments. For women with stage I, II, or III breast cancer, the main goal is to treat the cancer and prevent it from returning (curing). For women with stage IV cancer, the goal is to improve symptoms and help them live longer. In most cases, stage IV breast cancer cannot be cured.

• Stage 0 and DCIS -- Lumpectomy plus radiation or mastectomy is the standard treatment. There is some controversy on how best to treat DCIS.
• Stage I and II -- Lumpectomy plus radiation or mastectomy with some sort of lymph node removal is the standard treatment. Hormone therapy, chemotherapy, and biologic therapy may also be recommended following surgery.
• Stage III -- Treatment involves surgery, possibly followed by chemotherapy, hormone therapy, and biologic therapy.
• Stage IV -- Treatment may involve surgery, radiation, chemotherapy, hormonal therapy, or a combination of these treatments.

After treatment, some women will continue to take medications such as tamoxifen for a period of time. All women will continue to have blood tests, mammograms, and other tests after treatment.

Women who have had a mastectomy may have reconstructive breast surgery, either at the same time as the mastectomy or later.

Support Groups

Talking about your disease and treatment with others who share common experiences and problems can be helpful. See: Cancer support group

Expectations (prognosis)

New, improved treatments are helping persons with breast cancer live longer than ever before. However, even with treatment, breast cancer can spread to other parts of the body. Sometimes, cancer returns even after the entire tumor is removed and nearby lymph nodes are found to be cancer-free.

How well you do after being treated for breast cancer depends on many things. The more advanced your cancer, the poorer the outcome. Other factors used to determine the risk for recurrence and the likelihood of successful treatment include:

• Location of the tumor and how far it has spread
• Whether the tumor is hormone receptor-positive or -negative
• Tumor markers, such as HER2
• Gene expression
• Tumor size and shape
• Rate of cell division or how quickly the tumor is growing

After considering all of the above, your doctor can discuss your risk of having a recurrence of breast cancer.

Complications

You may experience side effects or complications from cancer treatment. For example, radiation therapy may cause temporary swelling of the breast (lymphedema), and aches and pains around the area.

Lymphedema may start 6 to 8 weeks after surgery or after radiation treatment for cancer.

It can also start very slowly after your cancer treatment is over. You may not notice symptoms until 18 to 24 months after treatment. Sometimes it can take years to develop.

Ask your doctor about the side effects you may have during treatment.

Calling your health care provider

Contact your health care provider for an appointment if:

• You have a breast or armpit lump
• You have nipple discharge

Also call your health care provider if you develop symptoms after being treated for breast cancer, such as:

• Nipple discharge
• Rash on the breast
• New lumps in the breast
• Swelling in the area
• Pain, especially chest pain, abdominal pain, or bone pain

Prevention

Tamoxifen is approved for breast cancer prevention in women aged 35 and older who are at high risk. Discuss this with your doctor.

Women at very high risk for breast cancer may consider preventive (prophylactic) mastectomy. This is the surgical removal of the breasts before breast cancer is ever diagnosed. Possible candidates include:

• Women who have already had one breast removed due to cancer
• Women with a strong family history of breast cancer
• Women with genes or genetic mutations that raise their risk of breast cancer (such as BRCA1 or BRCA2)

Your doctor may do a total mastectomy to reduce your risk of breast cancer. This may reduce, but does not eliminate the risk of breast cancer.

Many risk factors, such as your genes and family history, cannot be controlled. However, eating a healthy diet and making a few lifestyle changes may reduce your overall chance of getting cancer.

There is still little agreement about whether lifestyle changes can prevent breast cancer. The best advice is to eat a well-balanced diet and avoid focusing on one "cancer-fighting" food. The American Cancer Society's dietary guidelines for cancer prevention recommend that people:

• Choose foods and portion sizes that promote a healthy weight
• Choose whole grains instead of refined grain products
• Eat 5 or more servings of fruits and vegetables each day
• Limit processed and red meat in the diet
• Limit alcohol consumption to one drink per day (women who are at high risk for breast cancer should consider not drinking alcohol at all)

References

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