Subtypes of Breast Cancer

HER2-positive (HER2+)

HER2-positive breast cancers are known for the overexpression of the human epidermal growth factor receptor 2 (HER2) protein. HER2 proteins are receptors found on the surface of breast cells that are overexpressed in some breast cancers. In healthy cells, HER2 receptors are involved in controlling normal cell growth, division, and repair. In HER2-positive breast cancers, the cells overproduce the HER2 protein, which can result in uncontrolled division and growth of cells. An estimated 20 percent of breast cancers are believed to be HER2-positive.  These cancers are often treated with medicines targeted to the HER2 receptor, which has greatly improved the prognosis of this disease.

What is HER2-low?
Some breast cancer cells have low levels of the HER2 protein but not enough to be HER2-positive. HER2-low breast cancers may have the presence of the protein, but it is not driving the growth of the cancer in the same way as HER2+ breast cancers do. HER2-low breast cancers can make up about 50% of all breast cancer cases. This means that many patients with HER2-low breast cancer may have access to additional treatment options that were previously unavailable.

Systemic Treatments for HER2+ or low breast cancer
It is helpful to know your HER2 status as it can help you and your health care team decide if targeted systemic therapies are right for you. Systemic treatments are drugs that delivered to the entire body. These treatments are given orally in a pill format or using intravenous injection (IV).

HER2+ breast cancers can be treated with the following systemic therapies:

• Anti-HER2 targeted therapy: This type of targeted therapy specifically targets the HER2 protein by attaching to it, preventing the growth of cancer cells. Often combined with chemotherapy, these therapies lead to more effective treatment outcomes with potentially fewer side effects by targeting the HER2 protein.
• Chemotherapy: Chemotherapy destroys cancer cells, slows their growth, or stops them from spreading. It can be given through pill format or by IV. It can destroy both cancerous and healthy cells which is why side effects like hair loss are common.

For more information about potential treatment options, use our PatientPath tool to personalize information about your breast cancer, then navigate to the section titled “Making Treatment Decisions”.

Resources and Support
Here are some CBCN resources on HER2+ breast cancer:

• Questions & Experts: A Medical Oncologist Answers your Questions about HER2-positive Breast Cancer
• Advocacy Guide: Increasing Research on HER2-low Breast Cancer
• Our Voices Blogs on HER2+ breast cancers
• MedSearch: HER2+ treatments

Resources from Partner Organizations:

• Breastcancer.org: HER2 Status
• Living Beyond Breast Cancer: HER2-positive or HER2-low breast cancer
• HER2 Positive Breast Cancer Support and Awareness Group (private Facebook group not affiliated with CBCN)

References
Cancer Stat Facts: Female Breast Cancer Subtypes from the National Cancer Institute
Breast Cancer & You: A guide for people living with breast cancer by Canadian Breast Cancer Network
Advocacy Guide: Increasing Research on HER2-low Breast Cancer by Canadian Breast Cancer Network

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