Sentinel Lymph Node Biopsy

Sentinel Lymph Node Biopsy

Also known as SLNB

 What is a sentinel lymph node biopsy?

SLNB is the method used to classify a particular stage in cancer normally at or soon after the diagnosis stage.  This process entails evaluating the primary tumour (the T Stage), how much of the cancer has spread to the lymph nodes (N stage) and finally the spread of metastases to any other areas (the M stage).  SLNB is utilised during the N stage.

SLNB is a surgical procedure where the surgeon identifies and removes the first obvious sentinel lymph node for examination under the microscope for cancer cells.

There are three stages of the SLNB procedure.

  1. Lymphoscintigram, also known as lymphatic drainage scan or lymphatic mapping test is a medicine scan which is performed a day before the procedure. It involves an injection of a radioactive tracer around the tumour site and then lying quietly under the scanner for several periods of time over 2 hours.
  2. During this stage, the patient will be under general/regional anaesthesia, and a specialised blue dye is injected into the area surrounding the primary tumour. This dye will travel through the lymphatic vessels along the same route as the radioactive tag that was injected in stage 1, thereby assisting the surgeon in identifying the correct sentinel lymph node.
  3. The last stage involves the surgical removal of the identified sentinel lymph node. The excised lymph node will be sent to a pathologist for careful examination under the microscope to determine whether cancer cells are present.

When and why are sentinel lymph node biopsies performed? 

Sentinel lymph node biopsies are performed for malignant skin cancers, most frequently for melanomas.  SLNB can also be offered in the management of basal cell carcinomas of the head and neck and high-risk squamous cell carcinomas.

How is SLNB diagnosed?

A pathologist will examine the lymph node tissue obtained from the sentinel lymph node biopsy under a microscope. In some incidences, the pathologist may be able to give a diagnosis within 1-2 hours with a rapid fixing technique known as frozen section. However, the final diagnosis usually takes 2-3 days. Treatment decisions are based on the final diagnosis of the specimen.

How does cancer spread?

A malignant tumour usually spreads by three main routes:

  1. Local invasion of the surrounding tissue (horizontal and vertical expansion)
  2. Via the bloodstream, also known as haematogenous spread
  3. Through the lymphatic system

What are the side effects/complications of SLNB?

Immediate side effects:

  • pain & redness at injection site for approximately an hour
  • discolouration and staining of tissue around injection site which can take up to several weeks to resolve
  • blue/green discolouration of urine (up to 48 hours)
  • Possibility of allergic reaction to injected dye

This information has been written by Dr Linda Chan
Updated 12/02/2019


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