What are the different subtypes of MBC?

Each subtype of MBC has different characteristics. These subtypes are defined in large part by the status of estrogen and progesterone hormone receptors (HRs) and HER2 protein. The characterization of these markers in a tumor is used to inform treatment decisions. The subtypes are:

  • Hormone receptor-positive (HR+)
  • HER2-expressing
  • Triple-negative

What is hormone receptor-positive (HR+) breast cancer?

About 2 out of 3 breast cancers are HR+. These cancers have cells with receptors for hormones like estrogen and progesterone, which help the cancer grow.

HR Positive Breast Cancer Care HR Positive Breast Cancer Care
HER2 Breast Cancer Support HER2 Breast Cancer Support

What is HER2-expressing breast cancer?

HER2 protein expression in a tumor exists on a spectrum from low levels of HER2 expression to an overexpression of the HER2 protein. Cancers with higher-than-normal levels of HER2 protein expression are considered HER2-positive. When HER2 protein and receptors work normally, they control how a healthy breast cell grows, divides, and repairs itself. When there are too many, however, the cells grow rapidly and without control.

What is triple-negative breast cancer?

In this subtype, cancer grows in the absence of hormone receptors and without a higher-than-normal level of HER2 expression. In the United States, Black/African American women have more than double the risk of being diagnosed with triple-negative breast cancer than White women.

What is the typical treatment regimen for these subtypes?

  • HR+: A combination of endocrine and targeted therapy; however, people with rapidly progressing disease may receive chemotherapy in addition to endocrine therapy
  • HER2-expressing: Includes therapies that specifically target HER2 growth and may be combined with chemotherapy
  • Triple-negative: Chemotherapy, radiation therapy, and non-HER2 targeted therapy

You can learn more about treatment for these subtypes here.