Researchers have found several specific genetic mutations (changes) that lead to breast cancer. These changes can be detected through blood and tissue samples as tumor markers, which are created when genetic mutations result in cancer. Determining if tumor markers are present is known as molecular testing, and it’s likely your doctor will recommend it for staging, treatment and monitoring.
Molecular testing helps doctors diagnose a tumor, determine a prognosis (outlook), discover how aggressive (fast growing) the tumor is, predict response to treatment and monitor for a recurrence. In breast cancer, molecular marker testing is required for staging. This allows doctors to further classify breast cancer into subtypes, which may indicate the best treatment options for each diagnosis.
Tumor markers, also known as biomarkers, molecular markers, biological markers or serum markers, are substances produced by cancer cells or other cells in the body in response to cancer. These can include specific genes, proteins or molecules of the tumor. Breast cancer molecular marker (biomarker) testing is performed on the initial malignant biopsy material and is repeated if the breast cancer recurs.
To test your tumor, samples of your blood, tissue or other bodily fluids will be taken and sent to a laboratory where they are examined by a pathologist. The type of testing (and the type of tissue used for testing) will vary, depending on the type of cancer involved. Results are returned to your doctor.
Three tumor markers for breast cancer are routinely tested as part of the diagnostic process and help influence treatment options: estrogen and progesterone receptors (ER and PR) and human epidermal growth factor receptor-2 (HER2). Testing determines if ER, PR or HER2 is contributing to the cancer’s growth. Blocking these receptors with drugs can decrease tumor growth.
Other tumor markers found in breast cancer may be tested, including cancer antigens (CA 125, CA 15-3 and CA 27-29), carcinoembryonic antigen (CEA) and circulating tumor cells (CTC). These types of tumor marker studies are not typically performed with early-stage breast cancer.
Doctors may also test levels of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1), which are proteins found on cells that boost the immune system’s cancer-fighting response. These tests may determine if a woman with triple negative breast cancer (ER-, PR-, HER2-)is a candidate for immune checkpoint inhibitors, a type of immunotherapy approved to treat this specific breast cancer subtype (in combination with chemotherapy).
Understanding Tumor-agnostic Treatment
Molecular testing is also used to determine eligibility for tumor-agnostic treatment, which is a new class of drug therapy that treats solid tumors anywhere in the body that meet certain criteria:
- The tumors are metastatic or unresectable (cannot be removed with surgery).
- The tumor must contain a greater-than normal amount of molecular alterations.
- The cells must contain a mutation that prevents them from fixing errors that occur during duplication.
Genetic Counseling and Testing
Mutations passed from parent to child are known as hereditary cancer syndromes. The most common in women’s cancers is Hereditary Breast and Ovarian Cancer Syndrome. Knowing this type of information can empower you to make important decisions about your health.
The genes most commonly linked to breast cancer are BRCA1 and BRCA2 (breast cancer genes 1 and 2). Proteins produced by these genes normally repair damaged DNA. When mutated, the damaged DNA is not repaired, which may lead to additional cellular alterations that may become cancer. Research is ongoing to find other genes with links to various types of breast cancer.
If you are interested in genetic testing, it is highly recommended that you talk to your doctor or a genetic counselor who is trained to interpret the results.