A new technique to see if the melanoma has spread to the lymph nodes closest to the melanoma is called “sentinel node biopsy”. A substance containing a small amount of radioactivity is injected into the skin around the tumour. The substance passes into the lymph fluid and is trapped by the sentinel node. That lymph node can be removed and examined to see if there are any cancer cells in it. This technique is only used for thicker melanomas.

Examination of the “sentinel” lymph node or nodes in a patient with a primary melanoma on the skin very accurately indicates whether it has spread to the regional lymph nodes (e.g. in the groin, the armpit or the neck) has occurred. This means that patients who are at the highest risk of later developing melanoma-related problems are identified at an early stage of the disease. What is not yet clear is whether this earlier identification makes any difference to the ultimate outcome, and this is one of the important things that will be clarified by the results of the Multi-Center Selective Lymphadenectomy Trial*. It is also clear at this stage that the likelihood of a sentinel lymph node containing metastatic (secondary) melanoma cells is closely related to primary tumour thickness (routinely measured in millimetres by the pathologist).

The Sydney Melanoma Unit’s experience is that if the primary tumour is less that 1.5mm in thickness, the risk of the tumour having spread to the lymph nodes is 5%, if the primary tumour is between 1.5mm and 3mm the risk is 14%, and if the primary tumour is more than 3mm in thickness, the risk is 24%.

As expected, patients who have a sentinel node that contains melanoma cells are more likely to have subsequent melanoma-related problems, and all are offered a full regional lymph node dissection. The great challenge now is to find successful but non-toxic forms of additional treatment that will reduce the risk for patients with a positive sentinel node, or those who have not had a sentinel lymph node biopsy but who subsequently develop clinically recognisable, secondary disease in their lymph nodes.

Experience to date has shown that the sentinel node biopsy procedure can be technically difficult and it is therefore important that surgeons undertaking the procedure are appropriately trained and experienced.  Unless completely accurate identification of sentinel lymph nodes is achieved, misleading information may be obtained and inappropriate management decisions may be made.

At the Sydney Melanoma Unit we have been fortunate to have very high quality lymphatic mapping available using nuclear medicine techniques, thanks to the skill and enthusiasm of Associate Professors Roger Uren and Robert Howman-Giles. This lymphatic mapping (lymphoscintigraphy) allows the site of sentinel lymph nodes to be identified prior to surgery and greatly assists in the identification of these nodes at the time of surgery.   In addition, blue dye injection around the primary melanoma site is used to stain the sentinel lymph nodes, and it has been found that the greatest accuracy is able to be achieved at the time of surgery by using both blue dye staining and a small hand-held gamma probe (a mini Geiger counter) to identify the sentinel node or nodes.

Sentinel Node Biopsy Procedure

The sentinel lymph node biopsy procedure involves three steps:

1. a lymphoscintigram
2. intraoperative lymphatic mapping with blue dye
3. selective biopsy of lymph nodes identified as “sentinel” nodes

Lymphoscintigram

This is a nuclear medicine scan and is also referred to as a “lymphatic drainage scan” (or mapping test). This procedure is usually done the day before your operation. You do not have to fast before this test. The test accurately identifies the location of the lymph nodes that drain the field around the melanoma. This regional lymph node field might be at risk for containing metastatic disease.

A tiny dose of radioactive tracer is injected into the skin around the site of the primary melanoma. The tracer moves through the skin’s lymphatic channels and special scans are performed to determine the regional lymph node area to which drainage occurs.  The location of lymph nodes identified as “sentinel” nodes (a "sentinel node is the first node encountered on a lymph drainage pathway - if there is more than one pathway, there may be may be more than one sentinel node) will be marked on the skin with indelible ink (do not try to wash them off).

The side effects which may be associated with this scan are slight pain at the injection site during and shortly after the injection. You may also experience some redness at the injection site for an hour or two afterwards.

Click here to read more about lymphoscintigraphy.

Intraoperative Lymphatic Mapping

This procedure is performed in the operating theatre. A blue dye is injected into the skin around the site of the primary melanoma. The dye is rapidly absorbed into the lymphatic channels and moves to the regional lymph nodes. The dye assists in identifying the sentinel lymph nodes.

This procedure may be accompanied by discolouration of the injected skin and discolouration of the lymphatic channels leaving the injection site. There may be discolouration of the urine lasting no more than 48 hours. Although very rare, there is a possibility of allergic reaction to the dye.

Selective Lymph Node Dissection

This procedure is performed in the operating theatre at the same time as the surgical removal of additional skin and tissue around the site of the original melanoma. The “sentinel” nodes, identified by the blue dye in the lymphatic mapping procedure, are surgically removed and sent to pathology for examination. If melanoma cells are found to be present in a sentinel lymph node, it will be recommended that a complete lymph node dissection, which is the removal of all the lymph nodes in that region, be performed within 4-6 weeks.

Side effects which might accompany a selective lymph node dissection may include:

• pain and/or discomfort at the site of the incision

• loss of sensation in and around the site of the incision as well as the area immediately adjacent to the site

• fluid may collect at the incision site and might be accompanied by local infection.

• A small number of patients have temporary swelling of the limb. Occasionally this can persist as a longer term problem.