Sentinel Lymph Node Biopsy
What are lymph nodes?

There are two main networks of vessels that carry fluid in the body: blood vessels and lymph vessels (the lymphatic system). Lymph vessels transport milky fluid called lymph, which drains through lymph nodes. Lymph nodes entrap foreign or potentially harmful substances, such as bacteria and cancer cells. There are several hundred lymph nodes in each side of the neck. Groups of lymph nodes are easily felt around the neck when they become enlarged and sore during a cold or ‘flu. Other main groups of nodes are located in the groin (draining the leg), armpits (draining the arm), deep in the chest and abdomen.

What is the significance of lymph nodes in cancer?

Spread to the nearby lymph nodes (metastases) may reduce the chance of survival (prognosis), and the cancer may require different treatment.

How can your surgeon tell if cancer has spread to the lymph nodes?

If the cancer has spread, the nearby lymph nodes may be obviously enlarged and felt as firm or hard lumps. A fine needle aspiration biopsy may be performed through the skin and a small amount of tissue withdrawn by sucking it up a hollow needle. If confirmed, cancerous lymph nodes or metastases may be surgically removed neck (lymph node) dissection.


However, even if the lymph nodes appear to be normal, the cancer may have already spread to the lymph nodes. So in some cases, patients may be advised to have the draining lymph nodes removed and examined in case they have collected cancer cells. This prophylactic procedure is known as elective neck (lymph node) dissection. An alternative option in selected cases is sentinel node biopsy.

What is sentinel node biopsy… and what to expect?

Sentinel node biopsy is a surgical procedure that involves identification and biopsy of a sentinel lymph node, which is the very first lymph node to which lymph from the cancer site drains. Since it is not possible to identify the sentinel node with standard methods, this technique requires injection around the cancer of a radioactive material tracer (technetium – Tc), which drains to the sentinel node. The amount of technetium used results in less exposure to radiation than that received during a standard X-ray, and it disperses over a short time. A special scan (lymphoscintigram) performed prior to surgery demonstrates the position of the sentinel node. Your surgeon uses the lymphoscintigram and a radioactive scanner (Geiger counter) to locate the sentinel node. Your surgeon may also inject the cancer with blue dye, which drains to the sentinel node making it more easily identified by its blue colouring. A small cut is made into the skin overlying the area and the sentinel lymph node is removed. Sometimes more than one sentinel lymph node is detected in one or more body sites.


Sometimes the sentinel lymph node may not contain cancer while other lymph nodes do. If your surgeon is suspicious during the procedure he may remove other lymph nodes for pathological examination. If the primary cancer has not yet been removed, your surgeon will do so after stitching up the sentinel node biopsy wound. In some cases, the primary has been removed previously, but your surgeon performs a wider excision after the sentinel node biopsy. How much extra tissue is removed depends on the nature and thickness of the original cancer.


In most cases, you will be able to go home within a few hours of the surgery. After the procedure the blue dye is excreted from the body in the urine, which may appear green for few days. The stain at the surgery site fades away over a few months. The radioactive tracer dissipates over a short period of time.


Once removed, the sentinel node is sent for pathological examination. A result is usually available after a few days. However, the diagnosis of cancer is not always easy, and extra time may be required to perform special stains and/or seek other expert opinions. If there is no cancer in the sentinel lymph node, the cancer is very unlikely to have spread elsewhere, so no more lymph nodes need to be removed. If cancer is confirmed, further surgery may be required to remove more lymph nodes.


Sentinel node biopsy provides:

  • Accurate staging information that determines prognosis
  • Identification of patients that may benefit from specific therapy (eg neck dissection)
  • Identification of patients who do not require additional neck dissection surgery

When is sentinel node biopsy used?

Sentinel node biopsy in patients with head and neck cancer is a technique used by experienced and specifically trained head and neck cancer surgeons. It is not available to, nor is it appropriate for every patient with cancer. It is undertaken soon after the diagnosis of the cancer is made.


Sentinel node biopsy is sometimes recommended in patients with skin cancer:


Malignant-MelanomaMelanoma Sentinel node biopsy provides useful staging and prognostic information in some patients with primary melanoma. It is usually unnecessary in those with melanoma thinner than 1mm because the chance of metastasis is unlikely. In this group, even those in whom the tumour has ulcerated or the whole skin thickness is involved, the chance of positive nodes is less than 2%. Sentinel node biopsy is also not generally performed in those with melanoma thicker than 4mm because there is a high risk that metastasis has already occurred.

Squamous-Cell-CarcinomaSquamous cell carcinoma Sentinel node biopsy is most likely to be beneficial if the primary cancer is smaller than 4 to 5cm in diameter but deeper than 4 to 6 mm, and has not undergone previous surgery or radiotherapy that may have altered the flow of lymph vessels.

Basal-Skin-Cell-CarcinomaBasal cell carcinoma no value because of the extreme rarity of metastases.

Basal-Cell-Carcinoma-2Merkel cell carcinoma Sentinel node biopsy is recommended in some patients with Merkel cell carcinoma.

Tongue-UlcerHead and neck carcinoma Sentinel node biopsy is is also sometimes recommended for patients with other head and neck cancers, such as oral cavity cancer.

When is sentinel node biopsy unsuitable?

Sentinel node biopsy is not generally used in the following situations:


  • If the lymph nodes are enlarged.
  • If there is evidence of metastases at other body sites.
  • Following wide excision of the primary cancer, especially if a flap or graft has been used. This is because the lymphatic drainage may have been altered making the procedure inaccurate.
  • It may be difficult or impossible to perform a sentinel node biopsy when the primary cancer in the head or neck lies close to the draining lymph nodes.

What are the limitations of sentinel node biopsy?
  • The surgeon may be unable to find the sentinel lymph node.
  • The sentinel node biopsy result may be a false negative, i.e. following pathological assessment the sentinel node is reported to be normal but in fact cancer has already spread to other lymph nodes (about 3% of cases). In that case, the lymph nodes may become enlarged later on and need to be removed.
  • It might be a false positive i.e. the pathologist reports cancer, but in fact no cancer was present. This would result in unnecessary surgical removal of lymph nodes (neck dissection).
  • Sometimes, metastases may arise in distant sites of the body without involving the lymph nodes at all.

Complications of sentinel node biopsy

Complications specific to sentinel node biopsy relate to the blue dye. Rarely (less than 1%) develop a serious allergic reaction (anaphylaxis), or a blue tattoo at the injection site.


The main surgical complications include wound infection, bleeding from the wound, and poor wound healing, which are more likely in patients with diabetes, obesity, heart disease or that smoke.

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