This procedure was first studied in the treatment of penile cancer. The concept of a sentinel node being the first node to contain metastatic cancer within the tumour’s lymphatic basin was introduced by Cabanas in 1977. It was, however, not until the early 1990’s that it became the gold standard of care for evaluating the lymph nodes and for staging of early breast cancer. Sentinel lymph node biopsies are also used in the treatment of melanoma.
The technique is based on the hypothesis of stepwise distribution of cancer cells in the lymphatic system. The absence of cancer cells in the first lymph nodes/ glands in the direction of the lymphatic drainage of a cancer is thought to indicate the absence of further spread to higher lymph node basins. The first lymph node is therefore termed a sentinel node or guardian lymph node of the regional lymph node basin.
In order to find the sentinel lymph node, 2 procedures are required to localise these nodes. The patients will be required to undergo a nuclear medicine scan ( a Lymphoscintigram). This will usually be performed on the day of the operation.
A small injection of colloid particles labelled with technetium-99m will be injected into the nipple on the day of surgery. This injection does produce some stinging and discomfort at the site of injection , however, is rapidly resolves after approximately 30 seconds. The technetium tracer is transported through the lymph gland channels to the first lymph glands that drain the breast in the armpit.
When the patient arrives in the operating theatre after they are placed under a general anaesthetic, some patent blue dye will be injected into the nipple in order to further localise the sentinel lymph node. These nodes will be coloured blue and therefore Dr Thornton will be able to find the “blue and the hot nodes”. A gamma probe will be used in the operating theatre to detect the hot nodes. These are the nodes that will contain the colloid particles labelled with technetium-99m.
The blue dye will cause the nipple and areola to have some blue discolouration which will resolve and the patients will experience a colour change to their urine (blue urine).
Some patients may have an allergy to the blue dye however this is unusual. The allergic reaction can range from a blue hue to the skin, blue hives, or in the more serious and rare circumstances anaphylaxis. The patient will be under a general anaesthetic during the injection of the blue dye and will be carefully cared for by the anaesthetist during this process.
The false negative rate of sentinel lymph node biopsy has been quoted to range from 0- 10 percent. The procedure has been validated and is a highly reliable procedure for enabling the detection of lymph node invasion with minimal morbidity.
The benefits of sentinel lymph node biopsy are that only a few lymph nodes are removed and therefore the complications that can occur with a complete axillary lymph node dissection such as lymphoedema, shoulder stiffness, pain, and sensory changes to the arm and thoracic wall are significantly reduced.