Sentinel Node Biopsy For Breast Cancer

What is a "sentinel" node?

When a patient is diagnosed with breast cancer, it is important to find out if the cancer has spread. One of the first places that a breast cancer can spread to is the axilla (arm pit). As part of the staging and treatment of breast cancer, it is important to evaluate the lymph nodes in the axilla.

We have recently learned that there are certain lymph nodes that a tumor will spread to first before it spreads to any of the other nodes. This first node is called the sentinel node, and it may be in a different location in different patients. 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 breast cancer has spread to the lymph glands in the axilla. By injecting a slightly radioactive substance into the area around a tumor in the breast, 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.

There may be between one and five sentinel nodes. Because we only remove a small number of sentinel nodes the pathologist performs a more detailed examination of these nodes than the typical lymph node biopsy. 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 (in this case called an axillary dissection).

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 may be able to do only a sentinel node biopsy in some patients, and avoid a complete axillary dissection.

How is the sentinel node mapping done?
This is done in situations where we already know that a patient has a breast cancer, either because the patient has had a needle biopsy or a surgical biopsy. The day before the sentinel node biopsy procedure is done, the patient comes to the nuclear medicine department to have the area around the tumor (or biopsy site) injected with a small amount of substance called a radionucleotide. This substance will travel through the lymph channels to the sentinel node and make that node slightly radioactive. If the tumor can't be felt but only seen on mammogram, the radiologist will do the injection with ultrasound or mammography to guide the location of the injections.

How is the sentinel node biopsy done?
This is done under general anesthesia. 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 breast tumor will be removed (unless this has already been done during another procedure).
The remainder of the lymph glands in the armpit will be removed.

The pathologist will continue to process the lymph nodes after the surgery and will give us 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. This happens about 10% of the time.

Studies have shown that sentinel node biopsy is about 97% accurate in predicting whether the rest of the lymph glands in the axilla (armpit) will have cancer.

For some of the latest information on sentinel node biopsy, check the American Cancer Society web site.