Biomarkers to Guide Treatment for Metastatic Breast Cancer

July 20, 2015

To help doctors provide their patients with the highest quality care, the American Society of Clinical Oncology (ASCO) developed a new guideline on using biomarkers to guide the treatment of metastatic breast cancer. This guide for patients is based on ASCO’s most recent recommendations.

Understanding biomarkers

A biomarker is a substance that is found in the blood, urine, or body tissues of a person with cancer. It is made by the tumor or by the body in response to the cancer. A biomarker may also be called a tumor marker, and can be found in or on the tumor itself. Biomarkers help doctors learn more about a cancer.

Metastatic breast cancer is cancer that has spread beyond the breast to other parts of the body. For this type of breast cancer, a few specific biomarkers are often useful for selecting the appropriate treatment options. Specific examples are listed below.

Biomarkers for metastatic breast cancer

Your doctor may recommend testing the following biomarkers. More details about how your doctor uses this information to determine your treatment options can be found further below.

  • Estrogen receptor (ER) and progesterone receptor (PR). Breast cancer cells with ER and/or PR depend on estrogen and/or progesterone to grow. Testing for ER and PR is done to find out if a cancer is likely to be successfully treated with hormonal therapy that stops these hormones from helping the cancer grow. Hormonal therapy may also be called endocrine therapy. Examples of hormonal therapy used for metastatic breast cancer include the following:

    • Aromatase inhibitors, which include anastraozole (Arimidex), letrozole (Femara), and exemestane (Aromasin)

    • Fulvestrant (Faslodex)

    • Tamoxifen (Nolvadex)

    In addition, hormonal therapy is sometimes combined with another type of treatment. Learn more about testing for ER and PR and hormonal therapy for breast cancer.

  • Human epidermal growth factor receptor 2 (HER2). HER2 is a protein found in all breast cells, but at varying levels. When a breast cell has an abnormally high level of HER2, it can drive breast cancer growth and spread. Testing for HER2 helps doctors know if a cancer can be treated with anti-HER2 treatments. These are treatments that can stop HER2 from helping tumor cells grow and spread. Anti-HER2 treatments include the following:

    • Trastuzumab (Herceptin)

    • Pertuzumab (Perjeta)

    • Lapatinib (Tykerb)

    • Trastuzumab emtansine (TDM-1; Kadcyla)

    Learn more about HER2 testing and anti-HER2 therapy.

  • Cancer antigen 15-3 (CA 15-3), cancer antigen 27.29 (CA 27.29), and carcinoembryonic antigen (CEA). These biomarkers may be found in the blood of people with breast cancer. However, abnormal levels of these biomarkers may also be a sign of another condition that is not cancer.

Recommendations for using tumor markers to guide treatment

The following recommendations explain when your doctor may use tumor markers to guide your treatment for metastatic breast cancer. It’s important to remember that your doctor’s recommendations for your treatment will be based on many factors related to the cancer and your health, not just the biomarkers.

  • Testing the areas where the tumor has spread for ER, PR, and HER2 may be recommended. This is because the ER, PR, and/or HER2 status of a tumor may change once it has spread.

  • Treatment options and changes to treatment are primarily based on factors other than biomarkers, such as how much and where the tumor has grown and your overall health and treatment preferences.

  • CEA, CA 15-3, and CA 27.29 tests may be used to add to the information your doctor already has about the cancer. These results may help contribute to decisions about your treatment. However, these biomarkers generally should not be used alone to guide treatment or for monitoring how well treatment is working.

What This Means for Patients

If you have been diagnosed with breast cancer that has spread to other parts of the body, your doctor may recommend testing these areas for ER, PR, and HER2. The results of these tests will help your doctor learn more about the tumor. These biomarkers may give information on what therapies could be effective. However, the results of these tests are not the only factor your doctor considers when presenting your options for treatment. Your doctor also considers where and how much the cancer has spread and your overall health, the treatments you have already received, and your treatment preferences.

Talk with your doctor about the biomarker tests recommended for you, including how the results will be used.

Questions to Ask the Doctor

To help you learn more about biomarker testing for metastatic breast cancer and how the results affect treatment, consider asking your doctor the following questions:

  • What biomarker tests do you recommend? Why?

  • How are these tests performed?

  • How often do I need these tests?

  • What do the results of these tests mean?

  • What would cause the results of ER, PR, and HER2 testing to differ from the results from the original tumor?

  • How will the results affect my treatment and treatment options?

Helpful Links

Read the entire clinical practice guideline at  

Guide to Breast Cancer

Tumor Marker Tests