Each year, approximately 230,000 women in the U.S. and about 2,200 men are diagnosed with breast cancer. If you are diagnosed with breast cancer, it’s important that doctors get as much information as they can about your tumor so they can make the best recommendations to treat the cancer. This fact sheet provides an overview of the general diagnostic tests that help doctors understand your tumor type. It also describes newer tests that offer additional information for women with certain types of early-stage (stage I or II) breast cancer.
Understanding your tumor type
Tests performed on tumor samples give valuable information that helps guide treatment decisions for breast cancer. By examining tumor samples under a microscope, doctors can determine if the tumor is invasive or noninvasive (in situ). The tumor sample will also help identify your tumor’s grade—whether it is a fast-growing or slow-growing form of breast cancer—as well as the tumor’s hormone receptor status and HER2 status. All of these tests will inform your oncologist about your recommended treatment plan.
Sentinel node mapping also helps doctors determine if breast cancer cells have spread to other parts of the body. If the sentinel (first) lymph node is cancer free, the nearby lymph nodes may also be unaffected and left intact. Removing a patient’s lymph nodes can affect her quality of life because it increases her risk of lymphedema, a painful swelling of the arm.
Determining hormone status
Estrogen and progesterone receptors are structures present on the surface of some cancer cells. These structures allow estrogen and progesterone to enter the cells and encourage them to grow. Tumors that test positive for these structures are called hormone receptor-positive and might be successfully treated with hormonal therapy (e.g., tamoxifen or aromatase inhibitors). These treatments prevent estrogen from attaching to receptors on breast cancer cells. As a result, estrogen cannot get in the cells, and tumor growth is slowed. The treatments also reduce the amount of hormones circulating in the body that attach to estrogen or progesterone receptors. By blocking hormones, the treatments deprive tumor cells of the substances they need to grow.
HER2-positive breast cancers are breast tumors that make too much of a substance called HER2/neu, which speeds the growth of cancer cells. About 20 percent of breast cancers are HER2-positive. Drugs that target HER2/neu slow the growth of the tumor. Such drugs include trastuzumab (Herceptin) and lapatinib (Tykerb). Your breast cancer will be tested to identify if it is HER2-positive to determine the best treatment options.
Triple-negative breast tumors do not depend on estrogen, progesterone, or HER2 for their growth, and account for about 15 percent of all breast cancers. The standard treatments include surgery, radiation and chemotherapy. Researchers are looking for new ways to combine chemotherapy and targeted drugs to offer the most benefit to those living with triple-negative breast cancer.
Personalizing breast cancer treatment
Some of the newest tools for women with breast cancer are tests that estimate the likelihood of deriving a benefit from chemotherapy. Currently, there are two tests approved for estimating a patient’s risk of recurrence with early-stage breast cancer: Oncotype DX and MammaPrint.
Oncotype DX and MammaPrint are appropriate for women with stage I or II breast cancer that is hormone receptor-positive and will be receiving hormonal therapy. For those who are “on the fence” about embarking on a course of chemotherapy, these tests may provide sufficient information to make the decision clearer and easier. Both tests work by analyzing the genes in tumor tissue removed during surgery. The tests look for patterns of abnormal genetic activity to predict how the tumor will behave. Oncotype DX examines the activity of 21 genes to determine chance of recurrence, and MammaPrint looks at 70 different genes.
The National Cancer Institute is using Oncotype DX in a clinical trial called TAILORx to study recently diagnosed patients with hormone receptor-positive, HER2-negative breast cancer that has not spread to the lymph nodes.
The TAILORx study is just one example of how research is transforming the way that doctors treat breast cancer—that is, basing their treatment approach on the patient’s tumor. If doctors know in advance that a treatment won’t be of benefit, the patient could be spared unnecessary side effects from the treatment.