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Breast Cancer

Medically reviewed by Last updated on Feb 12, 2024.

What is breast cancer?

Harvard Health Publishing

Breast cancer is the uncontrolled growth of abnormal cells that can develop in one of several areas of the breast, including the

Breast cancer is considered invasive when the cancer cells have penetrated the lining of the ducts or lobules. That means the cancer cells can be found in the surrounding tissues, such as fatty and connective tissues or the skin. Noninvasive breast cancer (in situ) occurs when cancer cells fill the ducts or lobules but haven't spread into surrounding tissue.

These are the main forms of invasive breast cancer:

As more women have regular mammograms, doctors are detecting many noninvasive or precancerous conditions before they become cancer. These conditions include

A woman's risk of developing breast cancer increases with age; more than three out of four breast cancer cases occur in women over age 50. Other risk factors for breast cancer include:

Although breast cancer is about 100 times more common in women than in men, men can develop the disease.

Symptoms of breast cancer

Symptoms of breast cancer include

Diagnosing breast cancer

Your doctor will ask whether you have any risk factors for breast cancer, especially whether the disease runs in your family. He or she will then examine your breasts, looking for any signs and symptoms of breast cancer. These include a lump or thickening in your breast, nipple inversion or discharge, swelling or changes in breast contour, redness or dimpling of breast skin, and enlarged lymph nodes under your arm.

If your doctor discovers a lump or your screening mammogram detects an area of abnormal breast tissue, your doctor recommend additional tests for breast cancer. If you haven't yet had a mammogram, that may be the next step. But in other cases, the next step is an ultrasound or magnetic resonance imaging (MRI).

Ultrasound can confirm whether the lump is a solid tumor or a fluid-filled, noncancerous cyst. It can also be used to assess any abnormal areas found on a mammogram.

Although it is not routinely performed, MRI is used to assess abnormalities on a mammogram, get a more accurate estimate of a cancer's size, and check for other cancers. MRI can also be used for screening in woman at high risk of breast cancer. Examples include:

If the lump is solid, your doctor probably will recommend a breast biopsy. During a biopsy, a small amount of breast tissue is removed and analyzed in a laboratory. Sometimes, your doctor will recommend a biopsy without doing an ultrasound or MRI first.

A breast biopsy can be done in different ways. These include:

The type of biopsy your doctor chooses will depend on the location of the lump, its size, and other factors.

A specialist called a pathologist will examine the tissue under a microscope determine whether the tissue contains cancer cells. If it does, the pathologist can determine the type of breast cancer.

The pathologist will also assign a grade to the cancer. The grade indicates how closely the cancer cells resemble normal cells. A lower grade means that the cancer is slower-growing and less likely to spread; a higher grade means that the cancer is aggressive and likely to spread. The grade is one factor doctors consider when planning treatment. The pathologist may also determine how rapidly the cancer cells are dividing.

Depending on the type of biopsy and whether neighboring lymph nodes were removed, the biopsy report may include additional information. For example, the report may clarify how much the cancer has spread.

Another important step is to determine whether the cancer cells are "hormone-receptor positive" for estrogen and progesterone. Receptors allow specific substances, such as hormones, to latch on to the cell. Normal breast cells have both estrogen and progesterone receptors.

Cancer cells may have both receptors, one receptor, or no receptors. Women who have hormone-receptor positive cancers generally have a better prognosis. That's because they are more likely to respond to hormone therapy.

The biopsy sample should also be tested for a growth-promoting protein called HER2. The HER2 gene tells the cell to make the HER2 protein. Cancers with multiple copies of the HER2 gene produce too much HER2. These cancers, called HER2-positive, tend to grow and spread quickly.

This kind of information helps to guide treatment decisions. For example, women with HER2-positive cancers are likely to benefit from drugs that target the HER2 protein.

You may need to have additional tests to determine whether the cancer has spread. These include

Treatment options

The following list of medications are related to or used in the treatment of this condition.

View more treatment options

Expected duration of breast cancer

Breast cancer will continue to grow and spread until it is treated.

Preventing breast cancer

Although there are no guarantees, you can take steps to help prevent breast cancer:

Some women inherit mutations in the so-call breast cancer genes—BRCA1 and BRCA2. These genetic mutations put them at very high risk of developing breast and ovarian cancer. These women require more frequent screening, often with MRI. Some women opt to have their breasts and ovaries removed. This is the best way to prevent breast and ovarian cancer.

Treating breast cancer

Treatment for breast cancer usually begins with a decision about the type of surgery. Factors taken into consideration include:

A mastectomy removes the entire breast, usually with removal of some of the lymph nodes located in the axilla or arm pit. A lumpectomy removes only the cancerous tumor and a small amount of healthy tissue around it.

The cancerous breast tissue removed during surgery may undergo further analysis. This can include looking for certain molecular and genetic characteristics that sometimes influence decisions regarding additional therapy. In addition, the results may provide information relevant to cancer risk in family members.

After surgery, your doctor may recommend radiation therapy, chemotherapy, hormone therapy, targeted therapy, or a combination of therapies. Additional therapies decrease the risk of cancer returning or spreading. Radiation therapy usually is recommended after a lumpectomy to destroy any cancer cells left behind and to prevent the cancer from returning. 

The need for chemotherapy depends on how much the cancer has spread and the molecular characteristics of the cancer. In some cases, chemotherapy is recommended before surgery to shrink a large tumor so that it can be removed more easily. Chemotherapy is usually necessary if cancer returns.

Hormone therapy usually is recommended if the cancer is estrogen-receptor positive. The drug most often used in these cases is tamoxifen. It locks estrogen out of breast cancer cells that are estrogen-receptor positive. (Estrogen can help cancer cells grow.) This may reduce the chances that the cancer will return by up to 30%.

Aromatase inhibitors are another form of hormone therapy. These drugs decrease the amount of estrogen in the body by blocking estrogen production in all other tissues except the ovaries. Aromatase inhibitors are most useful in menopausal women, because the ovaries stop making estrogen after menopause.

Drugs that target specific genetic changes to attack cancer cells are called targeted therapies. For example, if you breast cancer is HER2-positive, your doctor may offer you trastuzumab (Herceptin). This drug is a manmade version of an immune system protein. It attaches itself to the HER2 receptor, slowing the growth of cancer. It may also stimulate your immune system to mount a stronger attack.

Other drugs are being developed that help in the treatment of women who carry a genetic trait that exposes them to a type of breast or ovarian cancer that runs in families.

There is current controversy regarding the best treatment for DCIS. Removal of the cancer by lumpectomy followed by radiation therapy has been the standard recommendation. However, for some women, complete removal of the area with a lumpectomy only may be sufficient. In cases where DCIS occurs in more than one location or if the tumor cells look especially worrisome on biopsy, the doctor may recommend mastectomy. Lymph nodes might also be removed as part of the mastectomy.

In most cases, LCIS has a lower likelihood of progressing to invasive cancer, so little or no treatment is required. However, women with this condition are more likely to develop cancer in other areas of the same breast or other breast. So they should have regular mammograms and breast exams. To decrease breast cancer risk, some women use hormone therapy, such as tamoxifen.

Based on your genetic markers, your doctor can choose the drugs that are most likely to attack your cancer. He or she may look to genetic markers to determine the chances that your breast cancer will spread to another site.

When to call a professional

Call your doctor immediately if you feel a lump or abnormal thickening in your breast. Call your doctor if you notice


Early diagnosis significantly improves the outlook for women with breast cancer. If the tumor is small and confined to the breast, more than 90% of women survive five years or longer. However, if the disease spreads throughout the body before diagnosis, that rate drops to less than 20%.

Cancer in one breast puts you at higher than average risk of developing cancer in the other breast. This is true even if you are still being treated with an estrogen blocker. Be sure to have regular checkups and mammograms.

Additional Information

National Cancer Institute (NCI)

American Cancer Society (ACS)

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.