Steven C. Immerman, M.D., FACS © 2000

What is a "sentinel" node?
A melanoma has the ability to spread to lymph nodes. This does not always happen, but when it does we want to be able to find and remove these lymph nodes. We have recently learned that in each individual case, there is a certain lymph node that a melanoma will spread to first before it spreads to any of the other nodes. This first node is called the sentinel node. It has been recently demonstrated that if the sentinel node is free of cancer, all the other lymph nodes will most probably be free of cancer as well.

This fact is being used to help us evaluate whether a melanoma has spread to the lymph glands in the armpit, groin or neck. By injecting a slightly radioactive substance into the area around the melanoma site, we can see which lymph glands concentrate this substance; this is called sentinel node mapping. This allows us to selectively biopsy those nodes. The biopsy itself is called a sentinel node biopsy.

For melanomas on the arms or legs, it is usually clear which lymph node area might be involved. For melanomas on the head, neck, chest or abdomen a melanoma can spread to several different areas, so sentinel node mapping is especially valuable. There may be between one and five sentinel nodes. Because we only remove a small number of sentinel nodes the pathologist performs a very detailed examination of these node. Because of this more detailed examination, we can learn more information about these few nodes than we may learn from the larger number that are removed in a complete node removal.

There are two reasons that sentinel node biopsy is considered beneficial for a patient:

• The sentinel nodes are examined in a more detailed fashion.
• We are able to do only a sentinel node biopsy in some patients, and avoid a complete node dissection. 

How is the sentinel node mapping done?
About an hour before we plan to start the operation the radiologist injects the area around the site of the melanoma with a small amount of substance we call a radionucleotide. This substance will travel to the sentinel node and make that node slightly radioactive.

After the injection, a lymphoscintogram will be done to see which lymph glands have concentrated the radionucleotide. This will give us a general idea of which lymph glands we have to be prepared to biopsy.

There are four parts to the operation:

• Location and biopsy of the sentinel node. This is done using a hand held Gamma Probe (which is like a Geiger counter) to find the radioactive nodes.
• A frozen section of this will be done and the pathologist will let us know if he sees cancer in the sentinel node(s). 
• The melanoma will be removed (unless this has already been done during another procedure).
• The remainder of the lymph glands will be removed in the area around the sentinel node in some situations.

The pathologist will continue to process the lymph nodes after the surgery and will issue a final report in two to three days. It is possible that he will not find cancer in the lymph nodes on frozen section, but will find evidence of cancer on his additional studies.