context: If you're diagnosed with breast cancer, your doctor may recommend the Oncotype DX. Depending on the type cancer you have, the test can tell doctors if it's likely to come back at some point. That helps with choosing the best treatment from the start. It's often one of the deciding factors on whether you have chemotherapy. The test doesn't require any further procedures for you. It uses tissue taken during the initial biopsy or surgery. It measures the breast cancer genes. ( You might hear it called a "21-gene signature.") Your doctor might suggest the test if you have: Stage I or II invasive breast cancer Estrogen-receptor positive (called ER+) cancer, meaning the disease's cells grow in response to the hormone estrogen Cancer that isn't in the lymph nodes You may also have it you've recently been diagnosed with ductal carcinoma in situ ( DCIS). It can help in deciding whether you have radiation treatments. The test looks at 21 different genes within the cells of a tumor sample. Certain patterns suggest a more aggressive cancer that is more likely to come back after treatment. The test results show a score between 0 and 100. If you don't have DCIS, the scoring is as follows: A score of 17 or smaller means you have a low risk of the cancer returning if you get a hormone treatment. With this score, you probably don't need chemotherapy to help prevent the disease from coming back. A score between 18 and 31 means you have a medium risk of cancer returning. Chemotherapy might help some women in this range. A score greater than 31 means you have a higher risk that the disease might come back. For women in this range, both chemotherapy and hormone therapy are likely to be recommended. If you've been diagnosed with DCIS, the results are called a DCIS score , and the numbers are different: A score of 38 or lower means you have a low risk of cancer returning, and the risks of radiation treatments outweigh any benefits for you. A score between 39-54 means you're at medium risk and it's unclear if radiation will help. A score greater than 54 means you're at high risk of the cancer coming back. You'll likely benefit most from radiation therapy. The results of your tests alone aren't enough to determine your treatment. Your doctor will also consider the tumor size and grade, the number of hormone receptors in your cancer, and your age before recommending a treatment plan. A large study called the TAILORx trial is under way with women who have a mid-range score. Researchers want more precise information on which types of breast cancer need chemo to stop them from coming back, and which cancers don't. Other genome tests show promise in helping treat early-stage breast cancer, but more research is needed. Mamma Print looks at 70 different genes within the cells of a breast tumor and helps predict whether cancer is likely to spread beyond the breast. This test can be used for tumors that are ER+ or ER-. The Mammostrat test measures five genes to determine the risk for early-stage hormone receptor-positive disease coming back. The Prosigna assay looks at early-stage hormone receptor-positive disease in postmenopausal women (with up to three positive lymph nodes). It analyzes 58 genes and calculates the risk of cancer coming back somewhere else in the body within 10 years of diagnosis after hormone therapy.