Subtypes of Breast Cancer

Triple Negative (TNBC)

Triple negative breast cancer (TNBC) refers to cancers whose growth is not driven by the hormones estrogen or progesterone or by the overexpression of HER2 (human epidermal growth factor receptor) proteins. Targeted therapies developed for hormone receptor-positive and HER2-positive breast cancers are often ineffective against triple-negative breast cancers. Chemotherapy, immunotherapy, surgery, and radiation are the most effective treatments currently available for TNBC.

Additionally, TNBC is associated with the following unique factors:

1. Age at diagnosis: While breast cancer is more commonly diagnosed in people over 50, TNBC is known to be more frequently diagnosed in younger patients.
2. Ethnicity: Black and Hispanic women are more likely to be diagnosed with TNBC, but further research is key to fully understanding this link.
3. Genetic mutations: TNBC is more commonly associated with genetic mutations, such as BRCA. 60-80% of breast cancer patients with a BRCA1 mutation have TNBC.
4. Higher risk of recurrence: TNBC is also considered a more aggressive type of breast cancer and has a higher risk of recurrence (meaning they are more likely to come back after treatment ends).

Systemic Treatments for TNBC
While HR+ and HER2+ targeted systemic therapies may not be effective for TNBC, there are options available. Systemic treatments are drugs that delivered to the entire body. These treatments are given orally in a pill format or using intravenous injection (IV).

• 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.
• Immunotherapy: Immunotherapy boosts the body’s immune system to recognize and attack cancer cells.
• PARP Inhibitors: PARP inhibitors are a type of targeted therapy that blocks enzymes involved in repairing damaged DNA in cells. By blocking these enzymes, cancer cells cannot repair themselves, leading to their death. This type of drug is known to be effective against BRCA mutated breast cancers.

About 50% or more of breast cancers, including many triple negative breast cancers (44%), are HER2-low, meaning there are low levels of the HER2 (human epidermal growth factor receptor) protein present on the cancer cells, but it is not driving the growth of the cancer. Low levels of HER2 may offer additional treatment options. Visit the HER2 section for more information.

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 TNBC:

• Webinar: Advancements in Care for Triple Negative Breast Cancer
• Questions and Experts Series: A Medical Oncologist Answers your Questions about TNBC
• Advocacy Guide: Increasing Research on HER2-Low Breast Cancer
• Advocacy Guide: Accessing Genetic Testing in Canada
• Our Voices Blogs on TNBC  
• Medsearch: TNBC treatments
• TNBC Project Report

Resources from Partner Organizations:

• Triple Negative Breast Cancer Foundation
• Breastcancer.org: Triple Negative Breast Cancer
• Olive Branch of Hope: An organization dedicated to supporting women of African-Caribbean Heritage and other women of culturally diverse backgrounds who have been diagnosed with cancer
• Every Breast Counts: an info hub for Black women in Canada by Women’s College Hospital and Olive Branch of Hope
• Expose TNBC
• Uncovering TNBC

References
Breast Cancer & You: A guide for people living with breast cancer by Canadian Breast Cancer Network
TNBC Project Report by Canadian Breast Cancer Network
PARP Inhibitors by Cancer Research UK
Advocacy Guide: Increasing Research on HER2-low Breast Cancer by Canadian Breast Cancer Network

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