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Sentinel Lymph Node Biopsy
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Sentinel Lymph Node Biopsy

A sentinel lymph node biopsy is a surgical procedure used to determine the stage of cancer by checking if cancer cells have spread to the first lymph node where the tumor is most likely to drain.

Overview

A sentinel lymph node biopsy (SLNB) is a surgical procedure that checks your lymph nodes for cancer cells. An SLNB is only performed if you have already been diagnosed with cancer. This procedure finds, removes, and checks the sentinel lymph node to determine the stage of your cancer. Cancer staging is usually based on the size of your tumor and whether the cancer has spread (metastasized) to nearby areas, lymph nodes, or other parts of your body. Knowing the stage of your cancer can help your health care provider plan the best treatment for you.

Your lymph nodes are located throughout your body, including your underarms, neck, chest, abdomen, and groin. They are part of the lymphatic system, which helps to protect you from illness and maintain healthy fluid levels in your body. Your lymph fluid carries cells throughout your body to help fight infections and may filter cancer cells. However, with certain cancers such as breast cancer and melanoma, cancer cells may spread to your lymph nodes.

The sentinel lymph node is the first lymph node where these types of cancers are most likely to spread. It is usually located near the original tumor site and may receive drainage from the tumor. Your provider tests this node to see if your cancer has spread; sometimes, you may have more than one sentinel lymph node.

What is it used for?

A sentinel lymph node biopsy is used to find out whether an early-stage cancer has spread through your lymphatic system. It is most often used for people who have breast cancer or melanoma and is usually done when the tumor is being removed.

What happens during the procedure?

The procedure may be done in a hospital or an outpatient surgical center and often includes lymphoscintigraphy (lymph node mapping) to locate the node. Steps include:

  • Your provider will apply medicine to numb the skin over the procedure area.
  • You will be injected with a small amount of a radioactive substance called a tracer near the tumor. You may also be injected with a blue dye that stains the lymph node, making it easier to see.
  • You will be given general anesthesia by an anesthesiologist to ensure you are unconscious and do not feel pain.
  • Once you are unconscious, a camera will take images of the area to record the location of the tracer.
  • The node will be removed and sent to a lab for a biopsy to be checked for cancer cells.
  • The original tumor is also usually removed during the procedure.

Preparation and Risks

You will likely need to fast for several hours before the test and may need to stop taking blood thinners, such as aspirin. Be sure to arrange for someone to take you home afterward.

Risks include:

  • Bleeding, pain, or bruising at the biopsy site.
  • A small risk of infection, which can be treated with antibiotics.
  • Rare, mild allergic reactions to the tracer.
  • A low risk of lymphedema (swelling of the arms or legs) if only the sentinel lymph node is removed; the risk increases with the number of nodes removed.

Note: Radiation exposure from the tracer is safe for most adults but can be harmful to a developing baby. Tell your provider if you are pregnant or think you may be pregnant.

Understanding Results

  • Positive results: Cancer was found in the sentinel lymph node and may have spread. Your provider may recommend removing and testing more lymph nodes.
  • Negative results: No cancer cells were found, and it is unlikely that the cancer has spread. You will not need to have any more lymph nodes removed.

Frequently Asked Questions

The most frequent issues are infection, bleeding, and temporary numbness or tingling from nerve irritation. Lymphedema can occur if lymphatic channels are disrupted. Surgeons reduce risk by using meticulous technique, applying sterile barriers, and sometimes placing a drain to manage fluid. Post‑operative compression garments and early mobilization also help prevent swelling.
During SLNB, a small amount of radioactive tracer (technetium‑99m) is injected near the tumor, and a blue dye may also be applied. A handheld gamma probe detects the radioactivity, while the dye stains the lymphatic vessels, allowing the surgeon to visually identify and remove the first draining node(s).
positive result usually leads to a completion axillary lymph node dissection or targeted radiation therapy to remove or treat remaining nodes. The exact plan depends on tumor type, size, and overall health; oncologists weigh the benefits of further surgery against potential side effects.
Most patients can return to light activities within a week, but strenuous exercise, heavy lifting, or prolonged standing should be avoided for 2–4 weeks. Swelling and discomfort typically subside within 2–3 weeks, and a gentle range‑of‑motion routine helps restore mobility.===
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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