About Breast Cancer > What is breast cancer?

What is breast cancer?

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Breast cancer is uncontrolled growth of abnormal cells in the breast. Breast cancer is one of many types of cancer, and it’s the second most common cancer after skin cancer (among women) in the United States. While women are much more likely to develop breast cancer than men, men can be diagnosed with breast cancer, too.

How does breast cancer happen?

Our bodies are made up of trillions of cells. Healthy cells grow and divide to form new cells as the body needs them. The cells die when they are damaged or old. In cancerous cells, abnormal changes in the genes that control cell growth can cause cells to divide out of control. The damaged or old cells don’t die as they should. Malignant is another word used to describe cancerous cells. These cells can sometimes form into groups, called tumors.

In some cases, cancer cells stay confined to the breast (sometimes called “local to the breast”). Over time, it’s possible for some cancer cells to invade the bloodstream or lymph system and travel to other parts of the body. Cancer spread to another part of the body is called metastasis.

If you or someone you love has been diagnosed with breast cancer, we know how overwhelming it can feel. For many people, it’s unexpected. But you’re never alone. LBBC is here for you with informationsupport, and community, no matter where you are on the diagnosis and treatment path.


Types of breast cancer

Breast cancers usually start in the lobules or ducts of the breast. The lobules are glands that make breast milk. Ducts carry the milk from the lobules to the nipple. Breast cancer in the ducts is called ductal carcinoma. In the lobules, it’s called lobular carcinomaCarcinoma means cancer that begins in the skin or tissues that cover internal organs.

There are two main types of breast cancer, noninvasive and invasive, that include carcinomas of the ducts and lobules.

Noninvasive breast cancer

Noninvasive breast cancer is called in situ carcinoma. In breast cancer, in situ means that the cancer hasn’t spread beyond the ducts or lobules. There is one kind of noninvasive breast cancer: ductal carcinoma in situ, also called DCIS. A diagnosis of DCIS means that cancer cells are found in the lining of the milk ducts. DCIS is also called intraductal carcinoma.

Lobular carcinoma in situ, also called LCIS, is a noninvasive breast change that can happen inside a breast lobule. Although LCIS has carcinoma in its name, it is not cancer. It is a high-risk marker of increased risk of developing breast cancer in the future. If left untreated, LCIS cells don’t usually spread beyond the lobule or become cancer. But having LCIS does increase the risk of developing an invasive breast cancer in the future.

Learn more about DCIS and LCIS.

Invasive breast cancer

Invasive means that the cancer has grown through the lining of a duct or lobule into the surrounding breast tissue. There are two types of invasive breast cancer:

  • Invasive ductal carcinoma (IDC) begins in the ducts and travels to, or invades, nearby breast tissue outside the ducts. IDC is the most common type of invasive breast cancer.
  • Invasive lobular carcinoma (ILC) begins in the lobules and invades nearby breast tissue.

Invasive breast cancer can also travel beyond the breast to lymph nodes and other parts of the body.

Visit the types of breast cancer page to learn more.

Characteristics of breast cancer cells

Breast cancer cells can have many different characteristics that can affect treatment choices. After a tissue biopsy, your doctor will share a pathology report with you that explains how the cells look and behave. You may see cell characteristics described as hormone receptor-positive or negative and HER2-positive or negative.

There are also breast cancers that are considered less common, including male breast cancerinflammatory breast cancer, and Paget’s disease. Still, these breast cancers have no less of an impact on a person:

  • Male breast cancer includes the same types of breast cancer that happen in women: DCIS, IDC, and ILC. In 2021, it was estimated that 2,650 men in the U.S. would be diagnosed with breast cancer.
  • Inflammatory breast cancer (IBC) is an aggressive type of invasive breast cancer. IBC symptoms are usually different than those of other types of breast cancer. IBC symptoms include swelling of the breast, redness on a large area of the breast, and thickened breast skin that may look like an orange peel. People with IBC don’t usually have a breast lump. These cancers are often mistaken for breast infection, but do not respond to antibiotics. This can delay diagnosis, so if you are having these symptoms, it’s important to talk with your doctor about testing for IBC.
  • Paget’s disease of the breast usually affects the nipple and the areola (the darker circle of skin around the nipple). Most people diagnosed with Paget disease also have at least one other tumor in the affected breast.


Common symptoms of breast cancer include:

  • A lump in the breast
  • Swelling of all or part of the breast
  • Skin dimpling or puckering
  • Breast or nipple pain
  • Nipple that turns inward
  • Red, dry, flaking, or thickened nipple
  • Nipple discharge that is not breast milk, with or without bleeding
  • Swollen lymph nodes under the arm or around collar bone
  • Pain in the organ if the cancer metastasizes

Learn more about symptoms of breast cancer.


Risk factors

Here are some of the things that can increase the risk of breast cancer. While some of these can’t be controlled, some can:

  • Being born female
  • Getting older (risk increases after age 55)
  • Personal history of certain breast conditions or breast cancer
  • Certain kinds of breast lesions (abnormal changes in the breast tissue that you or your doctor can feel, or that can be seen on an imaging test)
  • Family history of breast cancer
  • Inherited genetic mutations, such as BRCA1 or BRCA2
  • Radiation exposure to breasts or chest
  • Having dense breasts
  • Starting menstrual periods early
  • Beginning menopause at an older age
  • Having been exposed to diethylstilbestrol (a drug used to lower risk of miscarriage)
  • Lack of exercise
  • Post-menopausal weight gain
  • Drinking alcohol
  • Taking some kinds of hormone replacement therapy after menopause (if taken for more than 5 years)

Reducing the risk of breast cancer

Right now, there is no sure way to prevent breast cancer. But there are many things you can do to reduce your risk, including:

  • Avoiding or limiting alcohol use
  • Exercising on a regular basis
  • Keeping a healthy weight
  • Limiting use of birth control that uses hormones
  • Limiting postmenopausal hormone replacement therapy
  • Breastfeeding, if possible, if you have children

It’s important to talk with your doctor about your own personal risk of developing breast cancer, and how your choices about birth control, having children or not having children, breastfeeding, and using hormone replacement therapy might affect your risk.

What if I’m at high risk?

If you’ve had genetic testing and have tested positive for a gene mutation such as BRCA1 or BRCA2, or if you have a sibling or parent who has tested positive, you are considered to have a high risk for breast cancer.

There are risk-reducing options for people who live with a high risk, including using preventive medicines. Preventive medicines can include hormonal therapies such as tamoxifenraloxifene, or aromatase inhibitors. You and your health care team may also discuss the option of having prophylactic, or preventive, surgery, including mastectomy.

Learn more about our resources for high-risk and concerned individuals.



If tests, such as mammogram or ultrasound, suggest that breast cells could be cancerous, a doctor will likely recommend another test called a biopsy. During a biopsy, a doctor removes a small amount of breast tissue. The tissue sample is sent to a lab, where a pathologist (a doctor who analyzes tissue under a microscope) can look to see if the tissue has cancer cells. Sometimes more tests, such as MRI, are needed after a biopsy to get more information.

If cancer cells are found, they are tested to find out what makes the cancer grow, how fast it is growing, and whether the cancer is confined to the breast tissue or may have traveled to other areas of the body. The results are included in your pathology report. You and your doctors can use the information on the report to make treatment decisions.

You can learn more about mammograms, biopsies, and other tests in our section on testing. It’s also important to know that free or low-cost mammograms are available through programs such as the National Breast and Cervical Cancer Early Detection Program (NBCCEDP).

Breast cancer stages

Doctors use a system called staging after they diagnose cancer. The cancer’s stage describes:

  • The size of the cancer
  • Whether a lymph node or nodes near the breast contain cancer
  • Whether the cancer has spread to other parts of the body
  • Characteristics of the cancer, such as the presence or absence of hormone or HER2 receptors
  • The grade of the cancer, which describes how much the cancer cells look like normal cells

The stage of cancer helps doctors determine how serious the breast cancer is and how best to treat it. There are five stages of breast cancer: 0 to IV (4). In general, the lower the number, the less the cancer has spread.

Stage is one piece of information doctors use to understand how well a treatment might work for you and to determine prognosis information. Stage, along with other factors, including advances in treatment, is also used to estimate survival rates.

If you’ve been diagnosed with breast cancer and you’re concerned about survival rates, you’re not alone. Lots of people are. But it’s important to know that many factors are involved in looking at life expectancy, and it’s not possible to predict exactly how long someone with breast cancer will live. These factors include if, and how far, the cancer has traveled in the body and how the cancer is behaving. It’s also important to keep in mind that if you’re looking at numbers that represent survival rates (statistics), these numbers are related to people diagnosed and treated at least 5 years ago. Statistics help cancer researchers understand how breast cancer affects large groups of people, but not any individual person.

Not everyone is interested in reading about breast cancer prognosis. This is completely understandable. But if this topic is important to you, you can visit Breast cancer life expectancy to learn more.


Treatment options

Here are some of the most common treatment options for breast cancer:

  • Surgery removes as much breast cancer as possible and lets doctors know more information about the cancer. Types of surgery include lumpectomy and mastectomy.
  • Radiation therapy destroys cancer cells by directing high-energy x-rays at the cancer.
  • Chemotherapy destroys cells that are growing or dividing quickly, including cancer cells. Chemotherapy also affects healthy cells, which is why it often causes side effects.
  • Hormonal therapy blocks or lowers hormones that help hormone receptor-positive breast cancers to grow.
  • Targeted therapy interferes with cancer cell growth by targeting cancer cells that have certain proteins or markers, or by targeting a process in the body that helps cancer cells grow.
  • Immunotherapy uses the body’s immune system to find and destroy cancer cells.

For more information on the above treatments and more, visit Treatments.


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Reviewed and updated: November 20, 2021

Reviewed by: Regina Hampton, MD, FACS


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