Subtypes of Breast Cancer

Hormone Receptor-positive (HR+)

Hormone receptor-positive (HR+) breast cancer refers to cancers in which the cells have receptors (proteins located inside the cell) that can receive signals from hormones that drive cell growth. Breast cancer can be estrogen-receptor positive (ER+) if it has receptors for estrogen, or progesterone-receptor positive (PR+) if it has receptors for progesterone. A hormone receptor-positive tumour may have any of the following combinations of hormone receptors:

• ER+, PR+

• ER+, PR-
• ER-, PR+

HR+ breast cancers can further be classed into two different molecular subtypes: Luminal A and Luminal B:

• Luminal A: These HR+ breast cancers can be either ER+ and/or PR+, and HER2-negative. Luminal A breast cancers also have low levels of the Ki-67 protein. Ki-67 is a protein that is used to measure how fast cancer cells are dividing. A low ki-67 score typically indicates that these breast cancers are slower growing.
• Luminal B: These HR+ breast cancers can also be ER+ and/or PR+ and can be HER2-positive or negative. Most commonly, these breast cancers tend to be ER+, HER2+. Luminal B breast cancers have high levels of the Ki-67 protein, meaning they are typically faster growing.

Systemic Treatments for HR+ breast cancer
It is helpful to know your hormone status as it can help you and your health care team decide if hormonal therapies and other systemic treatments would be of benefit to you. Systemic treatments are drugs that are delivered to the entire body. These treatments are given orally in a pill format or by using intravenous injection (IV).

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

• Hormonal (also known as Endocrine) therapy: Hormonal therapy slows the growth and spread of cancer cells either by changing hormone levels in your body or by blocking the effects of hormones on breast cancer cells.
• Targeted therapy: Targeted therapy specifically targets and attacks cancer cells by focusing on specific molecules involved in the cancer's growth and spread, minimizing damage to healthy cells. This approach aims to be more precise and often has fewer side effects compared to traditional chemotherapy.
• Chemotherapy: Chemotherapy destroys cancer cells, slows their growth, or stops them from spreading. 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 HR+ breast cancer:

• Questions & Experts: A Medical Oncologist Answers your Questions about HR-positive Breast Cancer
• Our Voices Blogs on HR+ breast cancers
• MedSearch: HR+ treatments

Resources from Partner Organizations:

• Breastcancer.org: Breast Cancer Hormone Receptor Status
• Living Beyond Breast Cancer Webinar: Managing treatment side effects of anti-estrogen therapies
• Hormone Positive Breast Cancer Support

References
Breast Cancer & You: A guide for people living with breast cancer by Canadian Breast Cancer Network
Molecular Subtypes of Breast Cancer by Breastcancer.orgKi-67 proliferation index definition by National Cancer Institute

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