Sentinel node biopsy involves removing the first lymph node (or nodes) in the armpit to which cancer cells are likely to spread from the breast. It’s important that sentinel node biopsy is done by a surgeon who is trained and experienced in this method.

Sentinel node biopsy is usually done during breast surgery (breast conserving surgery or mastectomy). Sometimes it may be performed as a separate procedure. The length of time it takes to do sentinel node biopsy varies for individual women.

The sentinel node(s) removed from the armpit are examined by a pathologist. If there are cancer cells in the sentinel node, further surgery (axillary dissection) may be needed to remove more lymph nodes from the armpit to check how many lymph nodes are affected. If the sentinel node is examined during surgery, it may be possible to remove the remaining lymph nodes during the same operation. However, for many women, a second operation is needed.

In a small number of cases, it’s not possible to find the sentinel node at the time of surgery. In this situation, an axillary dissection will be recommended.

What is the sentinel node?

The sentinel node is the first lymph node to which breast cancer cells may spread outside the breast. Although some women may have one sentinel node, some may have two or three sentinel nodes. Usually the sentinel node is in the armpit (axilla). Sometimes the sentinel node is in another part of the body — for example, in the chest between the ribs under the breast or above or under the collarbone. View a picture of lymph nodes near the breast.

How is the sentinel node found?

There are different ways of finding the sentinel node. The best way is to use a combination of two substances — one is a low-grade radioactive fluid (isotope) and the other is a blue dye. The dye and radioactive fluid show the surgeon to which lymph node(s) breast cancer cells are most likely to travel.

Sometimes, either the blue dye or the radioactive fluid alone is used to look for the sentinel node. However, fewer studies have been done using blue dye or radioactive fluid alone to show whether these are as good at finding the sentinel node as the combined method.

What does the procedure involve?

The radioactive fluid (usually about 1–2 ml) is injected into the breast around the cancer or under the areola before surgery. A special scan is done to find out to which lymph node(s) the radioactive fluid has travelled. During surgery, the blue dye is also injected into the breast. The blue dye will travel to the lymph nodes via the lymphatic vessels and the sentinel lymph node(s) should turn blue.

The surgeon can see the blue sentinel node(s) and detect the radioactive substance using a type of Geiger counter called a gamma probe. The surgeon can then remove the sentinel node(s). If more than one sentinel node is found, all the sentinel nodes are removed. If another enlarged lymph node is found in the armpit without dye in it, the surgeon will usually remove this node as well. If the sentinel node is not in the armpit, the surgeon will remove it if this can be done safely.

Is sentinel node biopsy always accurate?

In a small number of women, the sentinel node doesn’t have cancer cells, even though there are cancer cells in other lymph nodes in the armpit. This is called a ‘false-negative result’.

A false-negative result sometimes occurs because lymphatic vessels running to the lymph nodes that have cancer cells in them are blocked by cancer cells. This means that the dye goes into other normal lymph nodes instead.

To minimise the chance of a false-negative result, the surgeon may remove any enlarged nodes that are found at the time of surgery, even if they do not contain the dye.

Side effects of sentinel node biopsy

Clinical trials have shown that sentinel node biopsy is associated with a lower risk of arm problems than axillary dissection. This means that the risk of numbness, shoulder stiffness and lymphoedema is lower than with axillary dissection.

There’s a small risk of allergic reaction to the radioactive fluid or blue dye used to find the sentinel node. Allergic reactions are usually mild and easily treatable.

Rarely, women may experience a severe allergic reaction (less than 1 in 5000 cases). A doctor may decide not to use the blue dye for sentinel node biopsy if there’s reason to think a woman may be at significant risk of allergy to the blue dye.

If blue dye is used to find the sentinel node, the urine may turn blue for 24 hours after surgery. The skin of the breast may also become blue but this will fade with time.

There will be some pain associated with sentinel node biopsy, and injection of the radioactive isotope sometimes stings.