What is Breast Cancer?

Cancer is caused by malignant (cancerous) cells that grow and multiply without control. Cancer that begins in any part of the breast is called breast cancer.

In breast cancer, the malignant cells can develop in the lobules or glands that make breast milk; this is known as lobular carcinoma. Or, the cancer cells can start in the ducts or tubes that carry the milk to the nipple; this is known as ductal carcinoma.

According to American Cancer Society estimates for 2023:

  • Breast cancer is the second-most common form of cancer in American women
  • About 13 percent of American women will develop invasive breast cancer
  • More than 297,000 American women are diagnosed with invasive breast cancer each year
  • About 43,700 American women die from breast cancer each year

Breast cancer types include:

  • Ductal carcinoma in situ (DCIS)
  • Invasive ductal carcinoma
  • Invasive lobular carcinoma
  • Inflammatory breast cancer
  • Paget disease of the nipple
  • Angiosarcoma
  • Phyllodes tumor

The National Cancer Institute has more information on these breast cancer types.

Learn about breast cancer in men

Breast Cancer Symptoms

Signs of breast cancer may be similar to symptoms associated with other medical conditions. Please consult your doctor if you notice any of the following:

  • A lump or swelling in or near the breast, including under the arm
  • Change in the size or shape of the breast
  • Thickening of breast tissue
  • Nipple inversion (in which the nipple is pulled inward)
  • Nipple discharge, particularly if bloody
  • Breast pain or tenderness
  • Puckering or dimpling of the breast skin
  • Scaliness or redness of the breast skin or nipple

Screening for Breast Cancer

Screening for cancer means testing for something abnormal before it makes you sick. This allows cancer to be found earlier. The earlier a cancer is found, the smaller—and more treatable—it is likely to be.

The two most common ways to screen for breast cancer are:

  • Breast exam: A doctor examines your breasts—as well as lymph nodes in your armpits—for lumps or thickening of breast tissue. All women should also perform a breast self-exam once a month
  • Screening mammogram: A set of breast X-rays is created to detect an abnormality

Diagnosing Breast Cancer

Diagnostic tests and procedures for breast cancer include:

  • Diagnostic mammogram: This test may be ordered to evaluate an abnormality in greater detail
  • Ultrasound: High-frequency sound waves are used to create images of the breast and locate lumps in the tissue
  • Breast magnetic resonance imaging (MRI): A powerful magnetic field and computer assistance are used to produce detailed pictures of the breast and regional lymph nodes
  • Biopsy: A surgeon removes a sample of breast tissue, which a pathologist then checks for cancer

Staging Breast Cancer

Following a diagnosis of breast cancer, further tests are done to determine the location or density of cancer cells. This process, known as staging, helps your doctor choose the best treatment for you.

Stages of breast cancer range from Stage I (early-stage cancer) to Stage IV (cancer is advanced and has spread to other parts of the body, or metastatic breast cancer). Tests and procedures include:

  • Mammogram
  • Breast MRI
  • Blood tests (e.g. blood count)
  • Computed tomography (CT) scan: Special X-ray equipment is used to produce multiple images of the inside of the body and a computer to join them together in cross-sectional views of the area being studied
  • Positron emission tomography (PET) imaging: An image of your body's metabolic activity is created, showing the rate at which your body's cells break down and use sugar
  • Bone scan: Your entire skeleton is scanned for spots in the bones that might be abnormal

Breast Cancer Treatment

Your care team will work with you to develop a treatment plan. This individualized plan will depend on many factors, such as the type and stage of breast cancer, your general health, and your treatment preferences.

Treatment may involve one or more of these options:

  • Surgery includes conventional and minimally invasive approaches to removing part of the breast (e.g. a lumpectomy) or the entire breast (a mastectomy). If you have a mastectomy, you may also choose to have breast reconstruction surgery
  • Radiation therapy, which may follow surgery, uses high-energy radiation beams to shrink or destroy tumors while sparing healthy tissue
  • Chemotherapy, which may be employed before or after surgery, kills cancer cells through the use of intravenous or oral drugs
  • Hormone therapy, which may follow surgery, is sometimes effective in treating breast cancers that are sensitive to hormones
  • Targeted therapy refers to a new generation of cancer drugs that target and interfere with the activity of specific proteins that drive tumor growth and spread

Getting Treated for Breast Cancer

View breast cancer treatment materials and factsheets.

Video: Understanding Breast Cancer Treatment Options

Learn more about breast cancer and meet Amy Comander, MD, medical director of the Mass General Cancer Center in Waltham and director of the Breast Oncology Program at Newton-Wellesley Hospital, who describes available breast cancer treatment options.