Hormone receptor-positive (HR+) MBC means the cancer cells have receptors for the hormones estrogen and/or progesterone. This means that these hormones can help HR+ cancer cells grow. HR+ MBC is typically treated with hormone therapy, which blocks the body’s ability to make or respond to these hormones.
For many people, hormone therapy can stop working over time, which causes tumors to grow while receiving hormone therapy. This is called resistance. Researchers are looking for ways to overcome resistance to hormone therapy. Many times, resistance happens when the tumor develops a mutation in a gene called ESR1, the gene for the estrogen receptor. New treatments, including oral SERDs and other drugs, target this mutation and help overcome resistance to hormone therapy.
Read below for more information about hormone therapy resistance and to find clinical trials studying new types of hormone therapy and different ways to give hormone therapy.
Introduction to Hormone Therapy Resistance
Overcoming Hormone Therapy Resistance
- Cancer Today Magazine: Doctors and patients can try several strategies to overcome hormone therapy resistance (scroll to “More Targeted Options”)
- Breastcancer.org: Elacestrant (Orserdu®) can treat people with hormone therapy resistance due to mutations in the ESR1 gene
- Breastcancer.org: Imlunestrant is an experimental oral SERD that may help overcome resistance to hormone therapy
- Breastcancer.org: A clinical trial showed that detecting ESR1 mutations before MBC starts to grow and switching to camizestrant, an experimental oral SERD, improves survival
- Breast Cancer Research Foundation: Drugs called PROTACs are being tested in clinical trials to overcome hormone therapy resistance (scroll to “Research to Improve Hormone Therapy for Breast Cancer”)
MBC Clinical Trials
- Metastatic Trial Search: Trials for Hormone Therapy
Last Modified on September 2, 2025