Did you know that some breast cancers can be defined as estrogen receptor low (ER-low) breast cancer?
When you’re first diagnosed, a pathologist runs a series of lab tests on the cancer cells to see what drives the breast cancer to grow. Estrogen receptor positive (ER positive) breast cancer cells have proteins that respond to signals from estrogen, telling the cells to grow. Your pathology report will tell you whether the cancer is ER positive, and how many cells in the tumor sample had estrogen receptors.
Right now, any breast cancer with at least 1% of tested cells showing estrogen receptors is considered ER positive. But researchers have found that ER positive cancers that have a low number of cells with estrogen receptors may respond differently to treatment. These breast cancers are called “ER-low.”
To learn more about reading your test results, understanding ER-low, and what current guidelines are for treating estrogen receptor low breast cancer, see below.
What Do My Test Results Mean?
- How to Read Hormone Receptor Test Results Breastcancer.org explains the two scales used to describe the number of estrogen receptors on cancer cells, and what different results mean.
What Do Current Guidelines Say?
- ASCO and CAP Release Updated Guideline on Estrogen and Progesterone Testing in Breast Cancer The ASCO and CAP guidelines state that every lab should define ER positive as at least 1% of tested cells showing estrogen receptors. They acknowledge ER-low as a distinct group, but for now, this group is treated the same as all other ER+ breast cancer.
Should ER Low Breast Cancers Be Treated With Hormonal Therapy?
- Prognostic and Predictive Value of Low Estrogen Receptor Expression in Breast Cancer This research team found that hormonal therapies may not work as well against ER-low breast cancers.
- Breast Cancer Guidelines Carve Out Category for Low ER Expression It’s unclear whether hormonal therapy is the best treatment option for ER low breast cancers because of a lack of research data. Experts say doctors should talk to people with ER low breast cancers about the pros and cons of getting hormonal therapy.
What Are The Treatment Options for ER-Low Breast Cancer?
- TNBC Clinical Trials For ER-Low Breast Cancer Breast cancers that have any number of estrogen receptors, including those defined as ER-low, are currently treated with hormonal therapies. But some clinical trials for triple negative breast cancer (TNBC) accept people with ER-low cancers. See trials on Metastatic Trial Search that are accepting participants who qualify as ER-low.
- Clinical Trials for ER Positive Breast Cancer People with ER-low breast cancer may also qualify for clinical trials for estrogen positive (ER+) breast cancer. See clinical trials for estrogen positive breast cancer on Metastatic Trial Search.