What is breast cancer?

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 spread 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 information, support, 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 carcinoma. Carcinoma refers to cancer that begins in certain layers of the skin or tissues in internal organs.

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

It’s important to know that lobular carcinoma in situ, also called LCIS, is not cancer. LCIS is a breast change that can happen inside a breast lobule. It is a marker of increased risk of developing breast cancer in the future.

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.

Invasive breast cancer

Invasive means that the cancer has grown through the lining of a duct or lobule into the surrounding breast tissue. One way doctors describe invasive breast cancer is based on the cells from which the cancer develops. There are many types of invasive breast cancer, but the two most common are:

• Invasive ductal carcinoma (IDC) begins in the ducts and spreads 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.

Some invasive breast cancers are a mix of ductal and lobular.

There are also other, less common types of invasive ductal carcinoma, including:

• Medullary ductal carcinoma: breast cancer that feels like spongy tissue rather than a distinct lump
• Mucinous ductal carcinoma: a tumor that contains cancer cells and mucous they produce
• Papillary ductal carcinoma: the tumor has small, finger-shaped structures called papules
• Tubular ductal carcinoma: the cancer cells appear as tiny tube-shaped structures

Invasive breast cancer can also spread 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.

• Hormone receptor-positive breast cancer is breast cancer that needs the hormones estrogen and/or progesterone to grow. These breast cancers are usually treated with hormonal therapy.
• HER2-positive breast cancer is breast cancer that makes too much of the HER2 protein, and too many HER2 receptors. While HER2-positive breast cancers can be more aggressive than other breast cancers, there are many effective anti-HER2 breast cancer treatments. Chemotherapy is usually a required part of treatment, either before or after surgery.
• Triple-negative breast cancer is invasive breast cancer that is negative for hormone receptors and HER2 receptors. These cancers grow and spread faster than other breast cancers. While treatment options for triple-negative breast cancer used to be limited to surgery, chemotherapy, and radiation therapy, more treatments are becoming available. Chemotherapy is usually a required part of treatment, either before or after surgery.

There are also breast cancers that are considered less common, including male breast cancer, inflammatory 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 2026, it is estimated that 2,670 men in the U.S. will 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.

Symptoms

Symptoms of breast cancer can include:

• A lump in the breast
• Swelling of all or part of the breast
• Skin dimpling or puckering
• Nipple that turns inward
• Red, dry, flaking, or thickened nipple
• Nipple discharge that is clear or bloody and occurs without any squeezing of the breast or nipple
• Swollen lymph nodes under the arm or around collar bone

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
• Talking with your doctor about the small increase in breast cancer risk when taking hormonal birth control
• Talking with your doctor about the small increase in breast cancer risk when taking hormonal birth control
• 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 tamoxifen, raloxifene, 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.

Diagnosis

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 and how fast it is growing. 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 can include:

• 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 specific features of the cancer — such as whether it has hormone or HER2 receptors, how certain genes in the cancer are behaving, and whether cancer has spread beyond the breast — help 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 spread 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, mastectomy, and lymph node removal to check for cancer spread.
• 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.