A sentinel lymph node biopsy (SLNB) is the removal of the sentinel lymph node to see if it contains cancer. The sentinel lymph node is the first lymph node in a chain or cluster of lymph nodes that receives lymph fluid from the area around a tumour. Cancer cells will most likely spread to these lymph nodes. There may be more than one sentinel node, depending on the drainage route of the lymph vessels around the tumour. This test may also be called sentinel node biopsy or sentinel lymph node dissection (SLND).
Why SLNB is done
SLNB is done to:
- see if cancer has spread from the primary tumour to the lymph nodes
- This information is used to determine the stage (the extent of cancer in the body).
- help plan treatment
- reduce the chance of lymphedema (buildup of lymph fluid) developing
- SLNB reduces, but does not completely eliminate, the risk of lymphedema.
SLNB is being done more often, particularly for breast cancer and melanoma, but it may not be available in all treatment centres. SLNB may also be done as part of a clinical trial with other cancers. Studies are still underway to understand the full usefulness of SLNB and whether it affects survival or reduces the chance of cancer coming back (recurring).
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How SLNB is done
An SLNB is usually done as an outpatient procedure in the nuclear medicine department of a hospital.
- The surgeon injects a radioactive substance (radiotracer), a blue dye or both into the tissue around the tumour or into the area from where the tumour was removed.
- The radiotracer is injected anywhere from 1–16 hours before the surgical procedure.
- It takes about 5 minutes for the blue dye to reach the sentinel nodes, so the dye is often injected in the operating room just before the surgery.
- The dye or radioactive substance is taken up by the lymph vessels. It travels along the lymph vessels draining the area around the cancer to the sentinel lymph node(s).
- A special scanning device detects the radioactivity in the sentinel lymph node(s), or the surgeon looks for the lymph node(s) stained blue.
- Sometimes, the sentinel lymph node cannot be identified.
- If the sentinel lymph node is positive or if it cannot be identified, then more lymph nodes will need to be removed.
- The surgeon makes a small cut (incision) over the node(s).
- The radioactive or blue lymph node(s) is removed and sent to the laboratory to be examined under a microscope by a pathologist (a doctor who specializes in the causes and nature of disease).
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What the results mean
The sentinel lymph node may be described as negative or positive.
- A negative sentinel lymph node means that cancer was not found in the lymph node. The rest of the lymph nodes are left in place.
- A positive sentinel lymph node means that cancer was found in the lymph node. Additional lymph nodes in the area may be removed.
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What happens if a change or abnormality is found
Results from a SLNB usually provide enough information for the doctor to decide whether or not surgery is needed. The doctor will also decide whether further tests or procedures are needed.
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Potential side effects of SLNB
Side effects can occur with SLNB, but not everyone has them or experiences them in the same way. Side effects can happen any time during, immediately after or a few days or weeks after the procedure. Most side effects go away after SLNB.
SLNB removes fewer lymph nodes than other lymph node dissections, so there are fewer side effects. After SLNB, a person may experience:
- pain
- bruising
- arm numbness
- urine coloured by the blue dye
- allergic reaction to the dye (rare)
- lymphedema
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Limitations of SLNB
There is a small chance that cancer cells are present in other lymph nodes, even if the sentinel lymph node is negative. This may mean that the person does not receive adjuvant therapy after surgery, and there is a greater chance of the cancer coming back (recurring).
A person should discuss the benefits and risks of SLNB with their doctor.
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