To plan an effective treatment strategy for you, your doctor needs to know if your breast cancer has spread to the lymph nodes. What Are Lymph Nodes? Lymph nodes are small, bean-shaped structures that filter out waste products from your lymphatic system, a network of channels and nodes that drain excess fluids from tissue. Bacteria and foreign particles are trapped within the lymph nodes and destroyed by the cells of your immune system. The lymph nodes closest to the breast are located under your arms and are called the axillary nodes. The nodes under your breastbone are called the internal mammary nodes. What Is Lymph Node Biopsy? In years past, we had no choice but to remove most of the underarm lymph nodes in an operation called axillary dissection. Today, we can often offer an approach that’s easier to tolerate and faster to recover from that also gets you back to normal day-to-day activities more quickly. During lumpectomy or mastectomy, we routinely perform what is called a sentinel node biopsy, in which we remove one or more lymph nodes under the arm to inspect for cancer cells. The sentinel node is the first node to which breast cancer cells travel after leaving the breast. We can determine which node or nodes these are by injecting a small amount of dye or radioactivity into the breast and tracking where it goes next. If the sentinel lymph node or nodes are free of cancer, we’ll leave the remaining axillary lymph nodes alone. This approach saves many women from the most troublesome potential side effect of more-extensive surgery: swelling of the arm, known as lymphedema. For women who have a mastectomy, removing the underarm lymph nodes is necessary if they contain cancer cells. However, research shows that removing the sentinel lymph nodes offers no benefit for women who have had lumpectomy and radiotherapy and who have only one or two sentinel nodes containing cancer. Our breast surgeons have developed specific guidelines to include these new findings in our treatment of patients.