Breast Cancer Tumor Marker Testing

Tumor markers are characteristics of cancer cells that can provide information to help treat different types of cancer. A variety of tests to identify breast cancer tumor markers can be performed.

Tumor marker testing provides vital information about the cancer at the cellular level. Together with physical characteristics, such as size, type and stage of the tumor, marker testing can help determine the appropriate medicine and timing of treatment needed to treat the disease most effectively.

Testing Tissue Samples

  • When a woman is diagnosed with breast cancer, her doctor will often obtain a tissue sample from the tumor and send it to a laboratory for testing; the doctor will then receive a report outlining the test results.
  • The American Society of Clinical Oncology (ASCO), the College of American Pathologists (CAP) and National Comprehensive Cancer Network (NCCN) have established guidelines regarding interpretation of tumor marker tests.
  • Genentech does not endorse any specific tests, but believes tests should be used only after they have been reviewed and approved by the U.S. Food and Drug Administration (FDA).

Who Should be Tested

  • Guidelines recommend that women with invasive breast cancer be tested for tumor markers.1,2
  • A woman who has already had a biopsy (a sample taken from the tumor for testing) and knows she did not receive a tumor marker test for a specific characteristic may request a tumor marker test from her doctor.
  • If a woman is told her sample is no longer being stored, she might consider requesting a new biopsy if her tumor is still present or if her breast cancer returns.
  • Women should ask their doctor for additional information about testing.

Types of Tumor Marker Tests for Breast Cancer

Human Epidermal Growth Factor Receptor 2 (HER2)

  • Assessment of HER2 status is needed to decide if HER2-targeted medicines are appropriate1.
  • Standard HER2 tests measure how many copies of the HER2 gene are present in tumor cells or how many HER2 receptors are on the surface of tumor cells; either method is appropriate for determining HER2 status.1
    • Fluorescence in-situ Hybridization (FISH) — a gene-based diagnostic test used to identify women whose breast cancer cells carry amplified HER2 genes and therefore make too much HER2 protein.1
    • Immunohistochemistry (IHC) — a protein-based diagnostic test used to identify women whose breast cancer cells overexpress the HER2 protein as a result of too many copies of the HER2 gene.1
    • Tests are available for assessing HER2 status using other technologies, but not all are FDA-approved.1
  • A tumor may be HER2-positive if the test shows a higher than normal number of HER2 genes or receptors.
  • Approximately 15 to 30 percent of breast cancers are HER2-positive.3

Estrogen and Progesterone Receptors (ER and PR)

  • Studies have shown that estrogen and progesterone, two of the female sex hormones, often contribute to the growth of breast cancer.
  • Knowledge of whether a tumor is positive or negative for the presence of estrogen or progesterone receptors is used for determining prognosis and selection for anti-hormonal therapy.

During the clinical development process for each of our potential breast cancer therapies, Genentech evaluates tumor markers that will help healthcare providers identify patients who might benefit from our medicines. Each of our breast cancer therapies in development is being studied with an existing test or a new test is being developed. Genentech is committed to identifying individual patients that may benefit from our medicines.