A tumor marker is a substance found in a person's blood, urine, or the tumor itself. It is produced by the tumor or the body in response to cancer. Your doctor may suggest tumor marker tests at various stages in the diagnosis and treatment of cancer. When used with other medical tests, a tumor marker test can provide helpful information about the cancer and its treatment.

Tumor markers for breast cancer may be used for one or more of the following reasons:

• To help plan treatment with regard to one of the following conditions:
  • To find out whether a patient has a cancer with a favorable prognosis (the behavior of the cancer and the patient's chance of recovery) and may not need additional treatment
  • To predict whether a specific treatment will successfully treat a patient
• To check how a patient is doing over time
• To learn the risk of developing cancer (not addressed in this patient guide)
• To find cancer before there are any signs or symptoms (not addressed in this patient guide)

The following breast cancer tumor markers are discussed in this patient guide:

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 hormone therapy, such as tamoxifen (Nolvadex).

Human epidermal growth factor receptor 2 (HER2). This protein is present in large amounts in 20% to 25% of breast cancers. Anti-HER2 treatments block HER2 to stop the growth of cancer cells. Testing for HER2 helps doctors know if a cancer can be treated with anti-HER2 treatments, such as trastuzumab (Herceptin), and in some cases, may suggest whether additional treatment with chemotherapy may be helpful.

Cancer antigen 15-3 (CA 15-3), cancer antigen 27.29 (CA 27.29), and carcinoembryonic antigen (CEA).These tumor markers are found in 50% to 90% of patients with metastatic breast cancer (cancer that has spread outside the breast). However, high levels may also be a sign of another condition that is not cancer. Some doctors monitor these tumor markers to find an early recurrence (the return of cancer after treatment) in patients who do not show any signs of cancer after surgery, radiation therapy, and/or chemotherapy. A doctor may also use this test to learn whether cancer treatment is working. Learn more about when testing for these tumor markers is not recommended [1].

Urokinase plasminogen activator (uPA) and plasminogen activator inhibitor (PAI-1). Higher-than-normal levels of these tumor markers in the cancer tissue may mean that the cancer is more aggressive (faster growing). Accurate tests of uPA and PAI-1 require a specific way of saving and storing the tissue, so these tests may not be as common as the other tumor marker tests mentioned in this guide. These tumor markers may be used to guide the use of chemotherapy after surgery for patients with node-negative breast cancer (meaning there is no cancer found in the lymph nodes).

Oncotype DX. This is a test that measures multiple genes at once to estimate the risk of breast cancer recurrence for patients with early-stage, ER-positive, node-negative breast cancer. Patients with a low Recurrence Score may only need to be treated with hormone therapy and can avoid chemotherapy.