Definition

A lab test that is used to help predict whether breast cancer will come back or spread to other parts of the body. The test looks at the activity level of 21 different genes in breast cancer tissue of people with early-stage (stage I, II, or IIIA) invasive breast cancer that is estrogen receptor (ER) positive, HER2 negative, and is either node-negative or has spread to 1 to 3 lymph nodes. If the test shows that there is a high risk that the cancer will spread or come back, treatment with chemotherapy may be needed to lower the risk. Also called Oncotype DX breast cancer assay.