The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on September 21, 2021.

About breast cancer

Breast cancer is the second most common cancer among women in the United States, behind skin cancer. An estimated 281,550 new cases of breast cancer will be diagnosed in U.S. women in 2021, according to the American Cancer Society. Breast cancer accounts for 15 percent of all new cancer diagnoses and 7 percent of all cancer deaths each year.

What causes breast cancer?

Breast cancer develops when cells in the breast mutate and grow out of control, forming a tumor. Exactly what causes breast cells to mutate isn’t known, but certain factors can increase the risk of this happening. Aging and genetics are the biggest contributors to a woman’s breast cancer risk.

Other factors that may increase a woman’s risk for developing breast cancer include:

  • Obesity
  • Breast density
  • Menstrual history
  • A sedentary lifestyle
  • Heavy drinking
  • Previous medical treatments

Learn more about risk factors for breast cancer

Who gets breast cancer

The risk for developing breast cancer increases with age. According to the National Cancer Institute:
  • The average age of a woman diagnosed with breast cancer is 62.
  • The average age of a woman who dies from breast cancer is 68.
  • Breast cancer is the most common cancer diagnosed in women between age 55 and 64.
  • About 10 percent of breast cancers occur in women younger than 45.

Women with a family history of breast cancer may be at a higher risk for developing the disease. For example:

  • Women whose mother, sister or daughter has or had breast cancer may have double the risk.
  • Women with a brother, father or son who has or had breast cancer also have a higher risk, as do women with a first-degree relative or multiple relatives who have or had ovarian cancer.
  • Women who have inherited mutations in the BRCA1 or BRCA2 gene are at higher risk.
  • Jewish women of Ashkenazi descent are more likely to have the inherited mutations in the BRCA1 or BRCA2 genes.

Other factors that may increase a woman’s risk for developing breast cancer include:

  • Obesity
  • Breast density
  • Menstrual history
  • A sedentary lifestyle
  • Heavy drinking
  • Previous medical treatments

Race and ethnicity may also factor into a woman’s risk of developing, as well as the risk of dying, from breast cancer.

  • White women are more likely to develop breast cancer than Black women, but Black women are more likely to die from the disease.
  • Black women account for more of the breast cancer cases among women under age 45, and make up a higher percentage of triple-negative breast cancer cases (a less common type of the cancer).
  • Asian, Hispanic and Native American women are less likely to develop breast cancer or die from breast cancer than Black or white women.

Breast cancer also occurs in men, but is very rare – male breast cancer accounts for 1 percent of all diagnoses. Approximately 2,650 American men will be diagnosed with breast cancer in 2021, according to the American Cancer Society.

Breast cancer symptoms

A lump, mass and change in the feel or position of the breast are among the most common symptoms of breast cancer. Other symptoms include:

  • Swelling, redness or inflammation
  • Changes in the nipple
  • Nipple discharge
  • Pain in the breast Itchy or irritated breasts
  • Changes in color
  • Peeling or flaky skin

It’s important to alert your doctor or health care provider as soon as you experience symptoms.

Learn more about symptoms of breast cancer

Types of breast cancer

Breast cancers share one main thing in common—they all begin in the breast. Most breast cancers start in the ducts that carry milk to the nipple, or in the “lobules,” where breast milk is made. However, there are many different types of breast cancer, and the distinctions between them can be difficult to understand. 

Breast cancer types are separated into two main groups: invasive or in situ (non-invasive). All kinds of breast cancer fall under one of these categories. 

In situ (non-invasive): When breast cancer is not invasive, it is most likely ductal carcinoma in situ (DCIS), a non-invasive type of breast cancer that starts in a milk duct and has not yet spread anywhere else. DCIS accounts for approximately 1 in 5 new cases of breast cancer. DCIS is also called stage 0 breast cancer, and most women have a positive prognosis at this stage. However, DCIS can progress and spread beyond the milk ducts, becoming invasive cancer.

Invasive: Invasive breast cancer refers to any breast cancer that spreads from the original site and “invades” other areas, like nearby breast tissue, lymph nodes or anywhere else in the body. Most breast cancers are invasive.

The most common type of invasive breast cancer is called invasive ductal carcinoma (IDC). IDC accounts for roughly 70 to 80 percent of all breast cancers. IDC starts in a milk duct and spreads, growing into other parts of the breast. With time, it may spread further, or metastasize, to other parts of the body.

Invasive lobular carcinoma (ILC) is the second most common type, accounting for roughly 5 to 10 percent of all breast cancers. ILC starts in lobules—where breast milk is made—and then spreads into nearby breast tissue. Like IDC, it can metastasize.

There are many other subtypes of invasive breast cancer—some are more challenging to treat or easier to treat than the more common IDC. Other, less common types of breast cancer include:

Types of invasive breast cancers

  • Triple-negative breast cancer is an invasive breast cancer that is hard to treat. About 15 percent of all breast cancers are triple-negative breast cancer.
  • Inflammatory breast cancer is a rarer type of invasive breast cancer. Roughly 1 to 5 percent of all breast cancers are inflammatory breast cancer.

Rare breast cancers that affect other types of cells in the breast, which are more aggressive and more challenging to treat:

  • Paget’s disease of the breast accounts for about 1 to 3 percent of all breast cancers.
  • Angiosarcoma accounts for about 1 percent of all breast cancers.
  • Phyllodes tumors make up less than 1 percent of all breast tumors, and the majority of them aren’t cancerous. However, these tumors tend to fall into one of three categories: benign (non-cancerous), malignant (cancerous) or borderline (somewhere between benign and malignant).

When breast cancer spreads out of the breasts and beyond nearby lymph nodes into other parts of the body, like the bones, lungs, liver or brain, it’s called metastatic, the most advanced breast cancer stage.

Breast cancer types may also be differentiated by other factors, which help determine the treatments that are most likely to work. Your doctor will identify these factors to come up with the most appropriate treatment plan for you. These factors include:

  • Where in the breast the cancer begins: Breast cancer may start in the ducts, the lobules or elsewhere in the breast (rarely).
  • Hormone receptor status: Hormone receptor status refers to whether breast cancer cells have specific proteins that act as “receptors” and attach to the hormones estrogen and progesterone. If a patient’s breast cancer cells have hormone receptors, then the cancer is hormone receptor-positive, which means the hormones estrogen and progesterone are responsible for fueling the cancer’s growth. If there are no receptors, the cancer is hormone receptor-negative. Hormone receptor status is determined by testing breast cancer cells that are removed during a biopsy or surgery. A cancer’s hormone receptor status will influence how it’s treated.
  • HER2 status. Breast cancers can be HER2-positive or HER2-negative, depending on the levels of a growth-promoting protein called HER2 within the cancer cells.
    • HER2-positive breast cancers have high levels of the HER2 protein, which means they are more likely to be fast-growing than some other types of breast cancer, but they may also be treated with drugs specifically designed to target the HER2 protein.
    • Cancers that are HER2-negative do not respond to the same drugs.

Learn more about breast cancer types

Diagnosing breast cancer

Diagnostic tests for breast cancer are used not only to determine if you have cancer but also to identify the type and how aggressive it is. Tools and tests used to diagnose breast cancer include:

  • Lab tests, including advanced genomic testing
  • Biopsy
  • Imaging tests, including ultrasound and mammography

Different tests are used to determine whether the breast cancer has metastasized. These tests include:

Learn more about diagnostic procedures for breast cancer

Creating a treatment plan

If you’ve been diagnosed with breast cancer, the next step will be to partner with your care team on treatment options. It's important to spend time learning about the benefits and risks of each approach Your care team—which may include an oncologist, nurses, social workers and other supportive providers—is there for you to learn from and lean on. 

  • Take notes about what you’ve learned, or ask a loved one to help write down questions and concerns.
  • Decide on a treatment plan jointly with your care team, when you’re ready. 
  • Don’t hesitate to seek a second opinion or ask about clinical trials. 
  • Consider joining a support group, where you can talk to other people who’ve also fought breast cancer. 

Understanding treatment options

There are two main categories of treatments for breast cancer and other types of cancer: local treatments and systemic treatments. 
  • Local treatments, like surgery and radiation therapy, focus on removing or attacking the tumor directly. 
  • Systemic treatments, like chemotherapy, hormone therapy, targeted therapy and immunotherapy, fight cancer throughout the body. 

Breast cancer treatment usually consists of a combination of local and systemic treatments. Most women with breast cancer have surgery to remove a tumor. But the other treatments used largely depend on factors like: 

  • The unique biology of the cancer 
  • The cancer’s stage 
  • Your health and age 
  • Your personal preferences 

Surgery is a common treatment option for breast cancer. Other treatment options include:

Learn more about treatment options for breast cancer