What type of breast cancer is most treatable with hormone testing?

From the Guidelines

Hormone receptor-positive breast cancer is the most treatable type of breast cancer with hormone testing, as it allows for targeted hormone therapy and significantly improves treatment outcomes. This type of breast cancer is typically characterized by estrogen receptor (ER) positive and/or progesterone receptor (PR) positive disease, and hormone testing plays a crucial role in identifying whether the cancer cells depend on hormones for growth. According to the ASCO guideline update on endocrine treatment and targeted therapy for hormone receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer 1, hormone receptor-positive metastatic breast cancer can be effectively treated with targeted therapies.

When testing reveals hormone receptor-positive status, treatments like tamoxifen, aromatase inhibitors (anastrozole, letrozole, exemestane), or fulvestrant can be used to block hormone effects or reduce hormone production, effectively slowing or stopping cancer growth. These therapies are often prescribed for 5-10 years and can substantially reduce recurrence risk. The reason hormone-positive cancers tend to be more treatable is that they provide a specific biological pathway that can be targeted, essentially cutting off the fuel supply that cancer cells need to grow, resulting in better long-term outcomes compared to triple-negative breast cancers which lack these targetable receptors.

Key points to consider in the treatment of hormone receptor-positive breast cancer include:

• The importance of hormone testing in identifying hormone receptor-positive status
• The use of targeted therapies such as tamoxifen, aromatase inhibitors, or fulvestrant to block hormone effects or reduce hormone production
• The potential for substantially reducing recurrence risk with long-term therapy (5-10 years)
• The improved treatment outcomes compared to triple-negative breast cancers. As noted in the ASCO guideline update 1, these factors contribute to the treatability of hormone receptor-positive breast cancer, making it a priority for hormone testing and targeted therapy.

From the FDA Drug Label

Among 29,441 patients with ER positive or unknown breast cancer, 58% were entered into trials comparing tamoxifen to no adjuvant therapy and 42% were entered into trials comparing tamoxifen in combination with chemotherapy vs. the same chemotherapy alone. Forty-eight percent of tumors were estrogen receptor (ER) positive (> 10 fmol/mg), 21% were ER poor (< 10 fmol/l), and 31% were ER unknown The effect of the scheduled duration of tamoxifen may be described as follows. In women with ER positive or unknown breast cancer receiving 1 year or less, 2 years or about 5 years of tamoxifen, the proportional reductions in mortality were 12%, 17% and 26%, respectively

The type of breast cancer that is most treatable with hormone testing is ER positive breast cancer. This is because the drug label shows that tamoxifen is effective in reducing mortality and recurrence in patients with ER positive or unknown breast cancer.

• Key points:
  • ER positive breast cancer shows a significant response to tamoxifen therapy
  • The proportional reductions in mortality for ER positive or unknown breast cancer were 12%, 17%, and 26% for 1 year or less, 2 years, or about 5 years of tamoxifen, respectively
  • The corresponding reductions in breast cancer recurrence were 21%, 29%, and 47% 2

From the Research

Type of Breast Cancer Most Treatable with Hormone Testing

• Hormone receptor-positive (HR+), human epidermal receptor 2 negative (HER2-) breast cancer is the most treatable type with hormone testing, as it responds well to hormone therapy 3, 4, 5, 6, 7.
• HR+ HER2- breast cancer accounts for the majority of breast cancer cases and has shown significant improvement in survival outcomes with the use of hormone therapy 4, 6.
• The European Society of Medical Oncology (ESMO), American Society of Clinical Oncology (ASCO), and National Comprehensive Cancer Network (NCCN) guidelines recommend hormone therapy as the primary treatment for HR+ HER2- advanced or metastatic breast cancer, unless in visceral crisis where chemotherapy is indicated 3.

Treatment Options for HR+ HER2- Breast Cancer

• Hormone therapy, including selective estrogen receptor modulator (SERM) or selective estrogen receptor down-regulator (SERD), aromatase inhibitor (AI), or their combination, is the mainstay of treatment for HR+ HER2- breast cancer 3, 6.
• Cyclin-D kinase 4/6 inhibitors (CDK4/6i) have shown significant efficacy in combination with AI or SERD in HR+ HER2- breast cancer, particularly in high-risk patients 3, 6, 7.
• Emerging data suggests that the addition of CDK4/6i to adjuvant endocrine therapy may improve outcomes in high-risk, HR+ HER2- early breast cancer 7.

Importance of Hormone Receptor Status

• Hormone receptor status is the most significant predictive and prognostic biomarker in breast cancer, and accurate testing is crucial for patient management 5.
• The definition of ER and PR positivity is 1% or more of cells that stain positive, and semiquantitative assessment of ER and PR is important for prognosis and management 5.