Breast cancer is a cancer that develops in the breast tissue. Abnormal breast cells (i.e. cancer cells) grow out of control, eventually forming a mass called a tumor. Triple-negative breast cancer means that the cancer cells do not contain proteins that are estrogen receptors or progesterone receptors and they do not make too much of a protein known as HER2. These three types of proteins fuel the growth of most breast cancers.

Approximately 15 to 20 percent of breast cancers are triple-negative, meaning they are estrogen receptor-negative, progesterone receptor-negative, and HER2-negative. These cancers grow and spread more quickly than most other breast cancers.

Triple-negative breast cancer is more common in:

  • Younger women
  • African-American women
  • Hispanic/Latina women
  • Women with a mutation in the BRCA1 gene

You may be at higher risk for any type of breast cancer if you have:

  • Had invasive breast cancer, ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS)
  • Had a benign (non-cancer) breast disease
  • Any first-degree relatives (mother, daughter, or sister) who had breast cancer
  • Inherited changes in the BRCA1 or BRCA2 genes (or other genes that increase breast cancer risk)
  • Breast tissue that is dense when viewed on a mammogram
  • Longer exposure of breast tissue to estrogen in the body from:
    • Menstruating at an early age
    • Older age at first birth or never having given birth
    • Starting menopause at a later age
  • Taken hormones such as estrogen combined with progestin for symptoms of menopause
  • Had treatment with radiation therapy to the breast or chest
  • Regularly consumed alcohol
  • Obesity

The symptoms of triple-negative breast cancer are the same as for other breast cancers. They include:

  • A new lump or mass in the breast
  • Swelling of all or part of the breast, even if there is no distinct lump
  • Irritation, dimpling or puckering of the skin on the breast
  • Pain in the breast or nipples
  • Nipple that is turned inward into the breast
  • Redness, scaliness, or thickening of the breast skin or nipple
  • Nipple discharge (possibly bloody) that is not breastmilk
  • Swollen lymph nodes under the arm or near the collarbone

Testing for Triple-Negative Breast Cancer

To diagnose any type of breast cancer, a sample of breast tissue (called a biopsy) is needed. A pathologist examines the biopsy tissue under a microscope to check for cancer cells. A needle biopsy removes a sample of the abnormal breast tissue through a needle. An excisional biopsy surgically removes part or all the abnormal tissue and often some surrounding normal tissue. 

Breast cells may have receptors that attach to estrogen and progesterone in the blood and depend on these hormones to grow. An immunohistochemistry test is used to determine if the cancer cells in the biopsy sample contain estrogen or progesterone receptors. If less than 1 percent of the cancer cells tested have these receptors, the cancer is classified as hormone-receptor negative.

HER2 is a protein located on the outside of breast cells that promotes cell growth. Immunohistochemistry stain or fluorescent in situ hybridization is used to test the biopsied cancer cells for HER2. Cancer cells with normal amounts of HER2 are called HER-2 negative. Cancer cells with higher amounts of HER2 are called HER2-positive.

Treating Triple-Negative Breast Cancer

Triple-negative breast cancer is usually treated with surgery to remove the tumor and chemotherapy before or after surgery, or possibly both.