Subtypes of Breast Cancer

Hormone receptor (HR) positive

Hormone receptor (HR) positive breast cancer occurs when cancer cells have hormone receptors that use estrogen or progesterone to help the tumour grow.

• Estrogen receptor (ER) positive: Cancer cells respond to estrogen
• Progesterone receptor (PR) positive: Cancer cells respond to progesterone

Tumours can have one or both receptors:

• ER positive / PR positive
• ER positive / PR negative
• ER negative / PR positive

Molecular Subtypes of HR Positive Breast Cancer

HR positive breast cancers are further classified into two molecular subtypes based on HR status, HER2 (human epidermal growth factor receptor 2) expression, and cell growth rate (Ki-67 levels).

Luminal A

• How common?: 50 - 60% of all breast cancers

• Receptor Status: ER positive and/or PR positive, HER2 negative
• Cell Growth: Low Ki-67 levels (a marker of cell growth)
• What it Means: Slow-growing, lower recurrence risk
• Treatment: Primarily hormone therapy; chemotherapy may not be needed
• Prognosis: Best overall prognosis

Luminal B

• How common?: 15 - 20% of breast cancers

• Receptor Status: ER positive and/or PR positive, HER2 positive or HER2 negative
• Cell Growth: High Ki-67 levels, indicating faster growth
• What it Means: More aggressive than Luminal A, with a higher recurrence risk
• Treatment: Often requires hormone therapy and chemotherapy; HER2-targeted therapy if HER2 positive
• Prognosis: Not as good as Luminal A, but still treatable

How Is HR Status Determined?

A HR status test checks if breast cancer cells have ER or PR, which influences tumour growth. It is performed on a biopsy sample using an immunohistochemistry (IHC) test.

The IHC test measures ER and PR levels and assigns a percentage score:

• 10% or more of cells are ER positive and/or PR positive → HR positive (likely to respond to hormone therapy)
• 1–9% are ER positive and/or PR positive → HR-low (uncertain hormone therapy benefit)
• Less than 1% are ER positive and PR positive → HR negative (hormone therapy is not effective)

Since HR status can change over time, repeat testing may be needed if cancer comes back.

Systemic Treatments for HR Positive Breast Cancer

Systemic treatments travel throughout the body and may be taken orally or intravenously (IV). These include:

Hormone Therapy
Also known as endocrine therapy, these drugs block or lower hormone levels to slow or stop cancer growth. There are different types of hormone therapy, and they work in different ways. The right choice depends on factors like whether you are pre- or post-menopausal.

• Estrogen Receptor Blockers: These block estrogen from attaching to cancer cells.
  • Tamoxifen (Selective Estrogen Receptor Modulator, SERM)
  • Fulvestrant (Selective Estrogen Receptor Degrader, SERD)
• Aromatase Inhibitors (AIs): These stop estrogen from being made in the body after menopause (post-menopause).
  • Anastrozole
  • Letrozole
  • Exemestane
• Luteinizing Hormone-Releasing Hormone (LHRH) Agonists: Also known as ovarian suppression, these drugs stop estrogen from being made by the ovaries before menopause (pre-menopause).
  • Goserelin
  • Leuprolide

Targeted Therapy
Targeted therapies block specific molecules that help cancer grow. These treatments often cause fewer side effects than chemotherapy. Most are used for HR positive metastatic breast cancer.

• CDK4/6 Inhibitors: These block proteins (CDK4 and CDK6) that help cancer cells grow and divide. Used with hormone therapy.
  • Abemaciclib (Verzenio)
  • Palbociclib (Ibrance)
  • Ribociclib (Kisqali)
• mTOR Inhibitors: Used with hormone therapy to block the mTOR protein that helps cell growth.
  • Everolimus (Afinitor)
• PI3K Inhibitors: These block part of the PI3K/AKT/mTOR pathway, which helps cancer cells survive and grow.
  • Alpelisib (Piqray)
  • Inavolisib (Itovebi)
• Antibody-Drug Conjugates (ADCs): These combine targeted therapy with chemotherapy delivering it directly to the cancer cells while sparing healthy tissue.
  • Sacituzumab govitecan (Trodelvy, SG)

Chemotherapy
Chemotherapy kills fast-growing cells, including cancer cells. It may also affect healthy cells, leading to side effects like hair loss.

Use our PatientPath tool to get information tailored to your diagnosis and visit the "Making Treatment Decisions" section to learn more.

Resources and Support

• 2025 Questions & Experts Session: Medical Oncologist, Dr. Omar Khan, Answers your Questions about HR+ Breast Cancer

• 2021 Questions & Experts Session: Medical Oncologist, Dr. Sandeep Sehdev, Answers your Questions About HR+ Breast Cancer
• MedSearch: Information on HR+ Treatment Options

Additional resources from partner organizations:

• Breastcancer.org: Breast Cancer Hormone Receptor Status
• Living Beyond Breast Cancer Webinar: Managing Treatment Side Effects of Anti-Estrogen Therapies
• Private Facebook Group: Hormone Positive Breast Cancer Support

Medical Review by Roochi Arora, MD, FRCPC, August 2025

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