What Does It Mean to Have Triple-Negative Breast Cancer?

An oncologist explains what makes this subtype unique.

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Although awareness of breast cancer has grown immensely in the 21st century, most people might be inclined to think of breast cancer as one single disease that affects everyone the same. Unless you or someone you know has had breast cancer, you might not realize that there are different types of breast cancer with unique qualities, all of which must be considered when choosing the appropriate treatment.

One category of breast cancer is triple-negative breast cancer (TNBC). To classify the type of breast cancer, doctors look for specific receptors on the surface of the cancer cells, according to Amy Tiersten, MD, oncologist at the Dubin Breast Center at Mount Sinai Hospital in New York City. These receptors fuel the growth of the breast cancer.

“There are three possible receptors,” says Dr. Tiersten. “Think of [receptors] as baseball mitts that sit on the surface of the cell. There are hormone receptors, estrogen and progesterone, and then there’s a protein called HER2.”

For example, some breast cancers will have estrogen receptors, which would be called a hormone receptor-positive breast cancer, while others might have HER2 receptors, which would be called a HER2 receptor-positive breast cancer.

“A triple-negative breast cancer just means that none of those three receptors are present,” says Dr. Tiersten. “[It’s] not that it’s triply bad, but that there are three possible receptors which are absent on those cells.”

Knowing which receptors are present on the cancer cells is important because it greatly impacts treatment options. Because the receptors impact cancer growth, therapies can target the receptors to shrink or eliminate breast cancer tumors.

Here’s how receptors on breast cancer cells influence treatment decisions:

  • Hormone receptor-positive breast cancer (which contain estrogen or progesterone receptors on the breast cancer cells) can be treated with hormone therapy.

  • HER2 receptor-positive breast cancer can be treated with targeted therapy for breast cancer that specifically goes after HER2 proteins.

  • Triple-negative breast cancer does not respond to neither hormone therapy nor targeted therapy because it is lacking all three receptors. It does, however, respond to chemotherapy better than other types of breast cancer. Learn more about treating triple-negative breast cancer here.

TNBC accounts for “about 15 to 20 percent of all breast cancers,” says Dr. Tiersten. “It’s associated with a younger-age diagnosis, [and] it’s a more common type of breast cancer among African American women.”

This type of breast cancer is also the most common among people who have the BRCA1 gene mutation, according to the National Cancer Institute. The BRCA1 gene is something everyone has, and it’s responsible for repairing DNA.

However, in some people, the BRCA1 gene undergoes a change (or mutation), and this makes the gene more likely to become cancerous. The BRCA1 mutation can also be inherited, so it runs in families. “About 80 percent of patients who have a BRCA1 mutation have triple-negative breast cancer,” says Dr. Tiersten.

Learn more about risk factors for all types of breast cancer here, and find out the things that probably don’t increase your risk of breast cancer here.