What is ER-Low Breast Cancer? - Metastatic Breast Cancer Trial Talk

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Pathology examination 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? 
What Do Current Guidelines Say?
Should ER Low Breast Cancers Be Treated With 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.

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