Breast surgeon Laurie Kirstein performs outpatient and short-stay procedures at the Josie Robertson Surgery Center. During a lymph node biopsy, a doctor removes lymph nodes to see if cancer cells have spread there. A sentinel node biopsy is the removal of a lymph node or nodes under the arm, called the axillary nodes, which are the first nodes to which cancer cells would travel if they were to leave the breast. This is where the fluid, or lymph, from the tumor flows. If cancer cells are traveling in the lymph system, the sentinel node is more likely than the other lymph nodes to contain them. This procedure is often done during a mastectomy or lumpectomy. To find the sentinel nodes, a special dye, a low dose of radioactivity, or both are injected into the breast. The nodes containing dye or radioactivity are the sentinel nodes, which are then removed and examined under a microscope. If no cancer is found, no other lymph nodes need to be removed, sparing you a bigger operation.  Learn more about lymph node biopsy