Sentinel lymph node biopsy (SLNB)

A sentinel lymph node biopsy (SLNB) is surgery to find and remove a sentinel lymph node to see if it contains cancer cells. A sentinel lymph node is the first lymph node in a chain or group of lymph nodes that cancer is most likely to spread to. There is often more than one sentinel lymph node.

An SLNB is also called sentinel node biopsy or sentinel lymph node dissection.

Why a sentinel lymph node biopsy is done

Many types of cancer can spread through the lymphatic system to the lymph nodes. There are groups of lymph nodes under the arms and in the neck, chest, abdomen and groin.

An SLNB is used to find out if cancer has spread to lymph nodes near where the cancer started. This helps your doctor stage the cancer, plan treatment and determine a prognosis. An SLNB is not usually done if the doctor can feel an enlarged lymph node or if tests show that the cancer has already spread to lymph nodes.

An SLNB is safer and has fewer side effects than removing all the lymph nodes in a specific area of the body (called a complete or therapeutic lymph node dissection). It also reduces the risk of swelling from the buildup of lymph fluid when lymph nodes are removed, damaged or blocked (lymphedema).

An SLNB is mainly used for breast cancers and melanoma skin cancers. It may be offered for other types of cancer, sometimes through a clinical trial. Clinical trials look at new ways to prevent, find and treat cancer. Researchers continue to study how an SLNB affects a prognosis and survival compared to other diagnostic tests or surgeries.

How a sentinel lymph node biopsy is done

On the day before or the same day as the SLNB, you will go to the nuclear medicine department of a hospital. You will have an injection of a radioactive substance (radiotracer) into an area close to the tumour or where the tumour was removed. This radioactive substance is absorbed by the lymph vessels and moves to the lymph nodes. A nuclear medicine doctor often uses a special imaging technique (lymphoscintigraphy) to take a picture and find the sentinel lymph node (or nodes).

An SLNB is usually done under general anesthetic in a hospital operating room as an outpatient (you will not stay overnight). It is usually done at the same time as surgery to remove the primary tumour. Just before the SLNB, the surgeon may inject a blue dye into an area close to the tumour or where the tumour was removed.

The surgeon uses a special probe to find the radioactive lymph nodes or looks for lymph nodes stained blue by the dye. The surgeon then removes the sentinel lymph node through a small cut (incision) in the skin above the group of lymph nodes closest to the primary tumour.

The sentinel lymph node is sent to a lab to be examined under a microscope.

Side effects

Side effects can happen if you have an SLNB, but everyone’s experience is different. Side effects can happen any time during, immediately after or a few days or weeks after an SLNB. Most side effects go away after an SLNB.

Side effects may include:

  • pain
  • bruising or swelling at the site of surgery
  • infection
  • numbness or tingling
  • lymphedema
  • problems moving a part of the body close to the site of surgery, such as an arm or shoulder
  • an allergic reaction to the dye

What the results mean

The results of an SLNB are often described as negative or positive.

A negative SLNB result means that cancer cells were not found in the sentinel lymph node. This is a normal result. The rest of the lymph nodes in the area are unlikely to contain cancer so they are not removed. But there is still a small chance that the cancer has spread to other lymph nodes when the result is negative (called a false-negative result).

A positive SLNB result means that cancer cells were found in the sentinel lymph node. This is an abnormal result. After an abnormal result, a lymph node dissection may be done to remove more lymph nodes from the area. Find out more about lymph node dissection.

Depending on the result, your doctor will decide if you need more tests, any treatment or follow-up care.

Expert review and references

Medical disclaimer

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