The lymphatic system is part of the immune system and one of the ways cancer cells can travel to other parts of the body. It’s made up of lymph nodes and vessels that carry lymph fluid throughout the body. The lymph nodes are small round organs that filter the lymph fluid. The sentinel node is the first lymph node that a tumor drains into. So, it’s the first place that cancer is likely to spread. In breast cancer, the sentinel node is usually one of the lymph nodes in the armpit. (These are called the axillary lymph nodes.)  A sentinel lymph node biopsy can be done at the same time as a lumpectomy or a mastectomy when there's no sign that cancer has spread to the lymph nodes. During the biopsy, one or more lymph nodes are removed. These are sent to the lab to be studied. If there are cancer cells in the sentinel node, this means the cancer has likely spread outside the breast, and more lymph nodes will need to be taken out. But if no cancer cells are found in the sentinel node, this means the cancer has probably not spread and the other lymph nodes can stay. A sentinel node biopsy gives the doctors valuable information about the cancer. There's also less risk and fewer side effects than with a full axillary lymph node dissection (when all the lymph nodes in the underarm are removed).

How is the sentinel node found?

There are 2 methods for finding the sentinel node. Your surgeon may use 1 or both of these techniques:

• A blue dye may be injected near the breast tissue. Then, its path into the lymph nodes is tracked. The dye collects in the sentinel node.
• A small amount of a safe radioactive solution may be injected near the tumor. A gamma detector is then used to find the “hotspot,” which is the node where the solution has collected.

Understanding the risks

Lymph node surgery involves certain risks. Your surgeon can discuss them with you. These include:

• Infection
• Bleeding
• Fluid collection (seroma)
• Pain or numbness (from damage to nearby nerves)
• Limited arm movement
• Long-term swelling of the arm (lymphedema)

Talk to your doctor about what you can do to help prevent these problems.

Sentinel lymph node breast biopsy is a complex surgical procedure. Make sure your surgeon has experience  doing this type of surgery.